diff --git a/base/src/main/java/io/spine/base/Environment.java b/base/src/main/java/io/spine/base/Environment.java
index f1a1ffd077..bfa8702caa 100644
--- a/base/src/main/java/io/spine/base/Environment.java
+++ b/base/src/main/java/io/spine/base/Environment.java
@@ -27,15 +27,16 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 import static com.google.common.base.Preconditions.checkNotNull;
+import static io.spine.util.Exceptions.newIllegalStateException;
 
 /**
  * Provides information about the environment (current platform used, etc.).
  *
  * <h1>Environment Type Detection</h1>
  *
- * <p>Current implementation allows to {@linkplain #is(EnvironmentType) check} whether a given
- * environment is currently the active one and {@linkplain #type() get an instance of the current
- * environment type}. Two environment types exist out of the box:
+ * <p>Current implementation allows to {@linkplain #is(Class) check} the type of the current
+ * environment, or {@linkplain #type() get the instance of the current environment}.
+ * Two environment types exist out of the box:
  *
  * <ul>
  *     <li><em>{@link Tests}</em> is detected if the current call stack has a reference to the unit
@@ -55,7 +56,7 @@
  *
  *     private Application() {
  *         Environment environment = Environment.instance();
- *         if(environment.is(Tests.type())) {
+ *         if(environment.is(Tests.class)) {
  *             // Do not send out emails if in tests.
  *             this.sender = new MockEmailSender();
  *         } else {
@@ -78,19 +79,19 @@
  *
  *     static {
  *         Environment.instance()
- *                    .register(StagingEnvironmentType.type())
- *                    .register(LoadTestingType.type());
+ *                    .register(new Staging())
+ *                    .register(new LoadTesting());
  *     }
  *
  *     private final ConnectionPool pool;
  *
  *     private Application() {
  *         Environment environment = Environment.instance();
- *         if (environment.is(Tests.type()) {
+ *         if (environment.is(Tests.class) {
  *              // Single connection is enough for tests.
  *             this.pool = new ConnectionPoolImpl(PoolCapacity.of(1));
  *         } else {
- *             if(environment.is(LoadTesting.type()) {
+ *             if(environment.is(LoadTesting.class) {
  *                 this.pool =
  *                         new ConnectionPoolImpl(PoolCapacity.fromConfig("load_tests.yml"));
  *             } else {
@@ -105,7 +106,7 @@
  *
  * <p><b>When registering custom types, please ensure</b> their mutual exclusivity.
  * If two or more environment types {@linkplain EnvironmentType#enabled() consider themselves
- * enabled} at the same time, the behaviour of {@link #is(EnvironmentType)}} is undefined.
+ * enabled} at the same time, the behaviour of {@link #is(Class)}} is undefined.
  *
  * @see EnvironmentType
  * @see Tests
@@ -115,7 +116,7 @@
 public final class Environment {
 
     private static final ImmutableList<EnvironmentType> BASE_TYPES =
-            ImmutableList.of(Tests.type(), Production.type());
+            ImmutableList.of(new Tests(), new Production());
 
     private static final Environment INSTANCE = new Environment();
 
@@ -133,7 +134,7 @@ private Environment(Environment copy) {
     }
 
     /**
-     * Remembers the specified environment type, allowing {@linkplain #is(EnvironmentType) to
+     * Remembers the specified environment type, allowing {@linkplain #is(Class) to
      * determine whether it's enabled} later.
      *
      * <p>Note that the default types are still present.
@@ -179,52 +180,46 @@ public Environment createCopy() {
      * goes through them in the latest-registered to earliest-registered order.
      * Then, checks {@link Tests} and {@link Production}.
      *
-     * @return the current environment type.
-     */
-    @SuppressWarnings("ConstantConditions"/* no NPE is ensured by the `ensureTypeIsSet` call. */)
-    public boolean is(EnvironmentType type) {
-        ensureTypeIsSet();
-        return currentEnvType.equals(type);
-    }
-
-    /**
-     * Returns the current environment type.
+     * <p>Please note that {@code is} follows assigment-compatibility:
+     * <pre>
+     *     abstract class AppEngine extends EnvironmentType {
+     *         ...
+     *     }
      *
-     * <p>If {@linkplain #register(EnvironmentType) custom env types have been defined},
-     * goes through them in the latest-registered to earliest-registered order.
-     * Then, checks {@link Tests} and {@link Production}.
+     *     final class AppEngineStandard extends AppEngine {
+     *         ...
+     *     }
      *
-     * @return the current environment type
+     *     Environment environment = Environment.instance();
+     *
+     *     // Assuming we are under App Engine Standard
+     *     assertThat(environment.is(AppEngine.class)).isTrue();
+     *
+     * </pre>
+     *
+     * @return whether the current environment type matches the specified one
      */
-    public EnvironmentType type() {
-        ensureTypeIsSet();
-        return currentEnvType;
-    }
-
-    private void ensureTypeIsSet() {
-        if (currentEnvType == null) {
-            determineCurrentType();
-        }
+    public boolean is(Class<? extends EnvironmentType> type) {
+        EnvironmentType currentEnv = cachedOrCalculated();
+        boolean result = type.isInstance(currentEnv);
+        return result;
     }
 
-    private void determineCurrentType() {
-        for (EnvironmentType type : knownEnvTypes) {
-            if (type.enabled()) {
-                this.currentEnvType = type;
-                return;
-            }
-        }
+    /** Returns the instance of the current environment. */
+    public EnvironmentType type() {
+        EnvironmentType currentEnv = cachedOrCalculated();
+        return currentEnv;
     }
 
     /**
      * Verifies if the code currently runs under a unit testing framework.
      *
      * @see Tests
-     * @deprecated use {@code Environment.instance().is(Tests.type)}
+     * @deprecated use {@code Environment.instance().is(Tests.class)}
      */
     @Deprecated
     public boolean isTests() {
-        return is(Tests.type());
+        return is(Tests.class);
     }
 
     /**
@@ -234,7 +229,7 @@ public boolean isTests() {
      *
      * @return {@code true} if the code runs in the production mode, {@code false} otherwise
      * @see Production
-     * @deprecated use {@code Environment.instance().is(Production.type())}
+     * @deprecated use {@code Environment.instance().is(Production.class)}
      */
     @Deprecated
     public boolean isProduction() {
@@ -271,7 +266,7 @@ public void setTo(EnvironmentType type) {
     @Deprecated
     @VisibleForTesting
     public void setToTests() {
-        this.currentEnvType = Tests.type();
+        this.currentEnvType = new Tests();
         Tests.enable();
     }
 
@@ -285,7 +280,7 @@ public void setToTests() {
     @Deprecated
     @VisibleForTesting
     public void setToProduction() {
-        this.currentEnvType = Production.type();
+        this.currentEnvType = new Production();
         Tests.clearTestingEnvVariable();
     }
 
@@ -298,4 +293,21 @@ public void reset() {
         this.knownEnvTypes = BASE_TYPES;
         Tests.clearTestingEnvVariable();
     }
+
+    private EnvironmentType cachedOrCalculated() {
+        EnvironmentType result = currentEnvType != null
+                                 ? currentEnvType
+                                 : currentType();
+        return result;
+    }
+
+    private EnvironmentType currentType() {
+        for (EnvironmentType type : knownEnvTypes) {
+            if (type.enabled()) {
+                return type;
+            }
+        }
+
+        throw newIllegalStateException("`Environment` could not find an active environment type.");
+    }
 }
diff --git a/base/src/main/java/io/spine/base/EnvironmentType.java b/base/src/main/java/io/spine/base/EnvironmentType.java
index 561b34a230..0c2719dd00 100644
--- a/base/src/main/java/io/spine/base/EnvironmentType.java
+++ b/base/src/main/java/io/spine/base/EnvironmentType.java
@@ -20,16 +20,12 @@
 
 package io.spine.base;
 
-import com.google.common.base.Objects;
-
 /**
  * A type of environment.
  *
  * <p>Some examples may be {@code STAGING} or {@code LOCAL} environments.
  *
- * @implNote developers are encouraged to make their environment types singletons, such
- *         that their API is consistent with the env types provided by the {@code base} library:
- *         {@link Production}, {@link Tests}.
+ * @implNote Not an {@code interface} to limit the access level of {@link #enabled()}
  */
 public abstract class EnvironmentType {
 
@@ -41,27 +37,4 @@ public abstract class EnvironmentType {
      * knowledge to determine the current environment.
      */
     protected abstract boolean enabled();
-
-    /**
-     * @inheritDoc
-     *
-     * <p>By default, environments types are compared based on their classes.
-     */
-    @Override
-    public boolean equals(Object obj) {
-        return this.getClass()
-                   .equals(obj.getClass());
-    }
-
-    /**
-     * @inheritDoc
-     *
-     * <p>By default, adheres to the {@code equals} and {@code hashCode} contract, assuming that
-     * the implementation of the {@code equals} is the {@linkplain EnvironmentType#equals(Object)
-     * default one}.
-     */
-    @Override
-    public int hashCode() {
-        return Objects.hashCode(getClass());
-    }
 }
diff --git a/base/src/main/java/io/spine/base/Production.java b/base/src/main/java/io/spine/base/Production.java
index 9f3ea652e9..a512549049 100644
--- a/base/src/main/java/io/spine/base/Production.java
+++ b/base/src/main/java/io/spine/base/Production.java
@@ -20,40 +20,25 @@
 
 package io.spine.base;
 
-import com.google.errorprone.annotations.Immutable;
-
 /**
  * A non-testing environment.
  *
  * <p>If the system is not in the {@link Tests} environment, it is in the production environment.
  */
-@Immutable
 public final class Production extends EnvironmentType {
 
-    @Override
-    protected boolean enabled() {
-        return !Tests.type()
-                     .enabled();
-    }
-
     /**
-     * Returns the singleton instance.
+     * Creates a new instance.
+     *
+     * <p>All {@code Production} instances are immutable and equivalent.
      */
-    public static Production type() {
-        return Singleton.INSTANCE.production;
+    public Production() {
+        super();
     }
 
-    private enum Singleton {
-
-        INSTANCE;
-
-        @SuppressWarnings({
-                "NonSerializableFieldInSerializableClass",
-                "PMD.SingularField" /* this field cannot be local */})
-        private final Production production;
-
-        Singleton() {
-            this.production = new Production();
-        }
+    @Override
+    protected boolean enabled() {
+        boolean tests = new Tests().enabled();
+        return !tests;
     }
 }
diff --git a/base/src/main/java/io/spine/base/Tests.java b/base/src/main/java/io/spine/base/Tests.java
index 2d55191c64..c9494e88f6 100644
--- a/base/src/main/java/io/spine/base/Tests.java
+++ b/base/src/main/java/io/spine/base/Tests.java
@@ -23,7 +23,6 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableList;
-import com.google.errorprone.annotations.Immutable;
 
 import java.util.regex.Pattern;
 
@@ -34,7 +33,6 @@
  *
  * <p>This option is mutually exclusive with {@link Production}, i.e. one of them is always enabled.
  */
-@Immutable
 @SuppressWarnings("AccessOfSystemProperties" /* is necessary for this class to function */)
 public final class Tests extends EnvironmentType {
 
@@ -53,14 +51,23 @@ public final class Tests extends EnvironmentType {
 
     private static final Pattern TEST_PROP_PATTERN = Pattern.compile("\"' ");
 
+    /**
+     * Creates a new instance.
+     *
+     * <p>All {@code Tests} instances are immutable and equivalent.
+     */
+    public Tests() {
+        super();
+    }
+
     /**
      * Verifies if the code currently runs under a unit testing framework.
      *
      * <p>The method returns {@code true} if the following packages are discovered
      * in the stacktrace:
      * <ul>
-     *     <li>{@code org.junit}
-     *     <li>{@code org.testng}
+     * <li>{@code org.junit}
+     * <li>{@code org.testng}
      * </ul>
      *
      * @return {@code true} if the code runs under a testing framework, {@code false} otherwise
@@ -99,25 +106,4 @@ static void clearTestingEnvVariable() {
     static void enable() {
         System.setProperty(ENV_KEY_TESTS, String.valueOf(true));
     }
-
-    /**
-     * Returns the singleton instance of this class.
-     */
-    public static Tests type() {
-        return Singleton.INSTANCE.tests;
-    }
-
-    private enum Singleton {
-
-        INSTANCE;
-
-        @SuppressWarnings({
-                "NonSerializableFieldInSerializableClass",
-                "PMD.SingularField" /* this field cannot be local */})
-        private final Tests tests;
-
-        Singleton() {
-            this.tests = new Tests();
-        }
-    }
 }
diff --git a/base/src/test/java/io/spine/base/EnvironmentTest.java b/base/src/test/java/io/spine/base/EnvironmentTest.java
index 9e6422eb88..d6e27579f5 100644
--- a/base/src/test/java/io/spine/base/EnvironmentTest.java
+++ b/base/src/test/java/io/spine/base/EnvironmentTest.java
@@ -20,6 +20,9 @@
 
 package io.spine.base;
 
+import com.google.errorprone.annotations.Immutable;
+import io.spine.base.given.AppEngine;
+import io.spine.base.given.AppEngineStandard;
 import io.spine.testing.UtilityClassTest;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
@@ -32,7 +35,6 @@
 import static com.google.common.truth.Truth.assertThat;
 import static io.spine.base.Tests.ENV_KEY_TESTS;
 import static org.junit.jupiter.api.Assertions.assertNull;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 
 @DisplayName("Environment utility class should")
 @SuppressWarnings("AccessOfSystemProperties")
@@ -83,11 +85,11 @@ void cleanUp() {
     @Test
     @DisplayName("tell that we are under tests if env. variable set to true")
     void environmentVarTrue() {
-        Tests tests = Tests.type();
+        Tests tests = new Tests();
         Environment.instance()
                    .setTo(tests);
 
-        assertThat(environment.is(Tests.type())).isTrue();
+        assertThat(environment.is(Tests.class)).isTrue();
     }
 
     @Test
@@ -95,14 +97,14 @@ void environmentVarTrue() {
     void environmentVar1() {
         System.setProperty(ENV_KEY_TESTS, "1");
 
-        assertThat(environment.is(Tests.type())).isTrue();
+        assertThat(environment.is(Tests.class)).isTrue();
     }
 
     @Test
     @DisplayName("tell that we are under tests if run under known framework")
     void underTestFramework() {
         // As we run this from under JUnit...
-        assertThat(environment.is(Tests.type())).isTrue();
+        assertThat(environment.is(Tests.class)).isTrue();
     }
 
     @Test
@@ -110,7 +112,7 @@ void underTestFramework() {
     void environmentVarUnknownValue() {
         System.setProperty(ENV_KEY_TESTS, "neitherTrueNor1");
 
-        assertThat(environment.is(Production.type())).isTrue();
+        assertThat(environment.is(Production.class)).isTrue();
     }
 
     @Test
@@ -127,7 +129,7 @@ void underTestFrameworkDeprecated() {
     void explicitlySetTrue() {
         environment.setToTests();
 
-        assertThat(environment.is(Tests.type())).isTrue();
+        assertThat(environment.is(Tests.class)).isTrue();
     }
 
     @Test
@@ -143,17 +145,17 @@ void inProductionUsingDeprecatedMethod() {
     @Test
     @DisplayName("turn tests mode on")
     void turnTestsOn() {
-        environment.setTo(Tests.type());
+        environment.setTo(new Tests());
 
-        assertThat(environment.is(Tests.type())).isTrue();
+        assertThat(environment.is(Tests.class)).isTrue();
     }
 
     @Test
     @DisplayName("turn production mode on")
     void turnProductionOn() {
-        environment.setTo(Production.type());
+        environment.setTo(new Production());
 
-        assertThat(environment.is(Production.type())).isTrue();
+        assertThat(environment.is(Production.class)).isTrue();
     }
 
     @Test
@@ -162,7 +164,7 @@ void turnProductionOn() {
     void turnProductionOnUsingDeprecatedMethod() {
         environment.setToProduction();
 
-        assertThat(environment.is(Production.type())).isTrue();
+        assertThat(environment.is(Production.class)).isTrue();
     }
 
     @Test
@@ -180,34 +182,58 @@ class CustomEnvTypes {
         @Test
         @DisplayName("allow to provide user defined environment types")
         void provideCustomTypes() {
-            register(Staging.type(), Local.type());
+            register(new Staging(), new Local());
 
             // Now that `Environment` knows about `LOCAL`, it should use it as fallback.
-            assertThat(environment.is(Local.type())).isTrue();
+            assertThat(environment.is(Local.class)).isTrue();
         }
 
         @Test
         @DisplayName("fallback to the `TESTS` environment")
         void fallBack() {
             Environment.instance()
-                       .register(Travis.type());
-            assertThat(environment.is(Travis.type())).isFalse();
-            assertThat(environment.is(Tests.type())).isTrue();
+                       .register(new Travis());
+            assertThat(environment.is(Travis.class)).isFalse();
+            assertThat(environment.is(Tests.class)).isTrue();
         }
     }
 
+    @Test
+    @DisplayName("follow assignment-compatibility when determining the type")
+    void polymorphicEnv() {
+        register(new AppEngineStandard());
+
+        AppEngineStandard.enable();
+        assertThat(environment.is(AppEngine.class)).isTrue();
+        AppEngineStandard.clear();
+    }
+
     @Test
     @DisplayName("detect the current environment correctly using the `type` method")
     void determineUsingType() {
-        assertThat(environment.type()).isSameInstanceAs(Tests.type());
+        assertThat(environment.is(Tests.class)).isTrue();
     }
 
     @Test
     @DisplayName("detect the current custom environment in presence of custom types")
     void determineUsingTypeInPresenceOfCustom() {
-        register(Local.type());
+        register(new Staging(), new Local());
+
+        assertThat(environment.is(Local.class)).isTrue();
+    }
 
-        assertThat(environment.type()).isSameInstanceAs(Local.type());
+    @Test
+    @DisplayName("return the instance of the default environment type")
+    void returnInstance() {
+        assertThat(environment.type()).isInstanceOf(Tests.class);
+    }
+
+    @Test
+    @DisplayName("return the instance of a custom environment type")
+    void returnCustomInstnace() {
+        register(new Local(), new Staging());
+
+        assertThat(environment.type()).isInstanceOf(Local.class);
     }
 
     private static void register(EnvironmentType... types) {
@@ -219,87 +245,31 @@ private static void register(EnvironmentType... types) {
 
     static final class Local extends EnvironmentType {
 
-        private Local() {
-        }
-
         @Override
         public boolean enabled() {
             // `LOCAL` is the default custom env type. It should be used as a fallback.
             return true;
         }
-
-        public static Local type() {
-            return Singleton.INSTANCE.local;
-        }
-
-        private enum Singleton {
-
-            INSTANCE;
-
-            @SuppressWarnings("NonSerializableFieldInSerializableClass")
-            private final Local local;
-
-            Singleton() {
-                this.local = new Local();
-            }
-        }
     }
 
     static final class Staging extends EnvironmentType {
 
         static final String STAGING_ENV_TYPE_KEY = "io.spine.base.EnvironmentTest.is_staging";
 
-        private Staging() {
-        }
-
-        public static Staging type() {
-            return Singleton.INSTANCE.staging;
-        }
-
         @Override
         public boolean enabled() {
             return String.valueOf(true)
                          .equalsIgnoreCase(System.getProperty(STAGING_ENV_TYPE_KEY));
         }
-
-        private enum Singleton {
-
-            INSTANCE;
-
-            @SuppressWarnings("NonSerializableFieldInSerializableClass")
-            private final Staging staging;
-
-            Singleton() {
-                this.staging = new Staging();
-            }
-        }
     }
 
+    @Immutable
     @SuppressWarnings("unused" /* The only variant is used. */)
     static final class Travis extends EnvironmentType {
 
-        private Travis() {
-        }
-
         @Override
         public boolean enabled() {
             return false;
         }
-
-        public static Travis type() {
-            return Singleton.INSTANCE.travis;
-        }
-
-        private enum Singleton {
-
-            INSTANCE;
-
-            @SuppressWarnings("NonSerializableFieldInSerializableClass")
-            private final Travis travis;
-
-            Singleton() {
-                this.travis = new Travis();
-            }
-        }
     }
 }
diff --git a/base/src/test/java/io/spine/base/environment/EnvironmentTest.java b/base/src/test/java/io/spine/base/environment/EnvironmentTest.java
index 299e6d4ad9..68ad0445c5 100644
--- a/base/src/test/java/io/spine/base/environment/EnvironmentTest.java
+++ b/base/src/test/java/io/spine/base/environment/EnvironmentTest.java
@@ -41,21 +41,20 @@ void reset() {
     @DisplayName("allow a custom user type")
     void allowCustomType() {
         Environment.instance()
-                   .register(Staging.type());
+                   .register(new Staging());
 
         Staging.enable();
         assertThat(Environment.instance()
-                              .is(Staging.type())).isTrue();
+                              .is(Staging.class)).isTrue();
     }
 
     @Test
     @DisplayName("fallback to the default type")
     void fallbackToCustomType() {
-        Environment.instance().register(Staging.type());
+        Environment.instance().register(new Staging());
 
         Staging.disable();
 
-        assertThat(Environment.instance().is(Tests.type())).isTrue();
+        assertThat(Environment.instance().is(Tests.class)).isTrue();
     }
-
 }
diff --git a/base/src/test/java/io/spine/base/environment/Staging.java b/base/src/test/java/io/spine/base/environment/Staging.java
index f436b35cdb..b49ea07486 100644
--- a/base/src/test/java/io/spine/base/environment/Staging.java
+++ b/base/src/test/java/io/spine/base/environment/Staging.java
@@ -30,35 +30,28 @@
  */
 public final class Staging extends EnvironmentType {
 
-    @Override
-    protected boolean enabled() {
-        return Singleton.INSTANCE.enabled;
+    private static boolean enabled = false;
+
+    Staging() {
+        super();
     }
 
-    public static Staging type() {
-        return Singleton.INSTANCE.staging;
+    @Override
+    protected boolean enabled() {
+        return enabled;
     }
 
     /**
      * Brings the underlying system into the staging environment.
      */
     static void enable() {
-        Singleton.INSTANCE.enabled = true;
+        enabled = true;
     }
 
     /**
      * Brings the underlying system out of the staging environment.
      */
     static void disable() {
-        Singleton.INSTANCE.enabled = false;
-    }
-
-    public enum Singleton {
-
-        INSTANCE;
-
-        @SuppressWarnings("NonSerializableFieldInSerializableClass")
-        private final Staging staging = new Staging();
-        private boolean enabled;
+        enabled = false;
     }
 }
diff --git a/base/src/test/java/io/spine/base/given/AppEngine.java b/base/src/test/java/io/spine/base/given/AppEngine.java
new file mode 100644
index 0000000000..3c049d31ba
--- /dev/null
+++ b/base/src/test/java/io/spine/base/given/AppEngine.java
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2020, TeamDev. All rights reserved.
+ *
+ * Redistribution and use in source and/or binary forms, with or without
+ * modification, must retain the above copyright notice and the following
+ * disclaimer.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package io.spine.base.given;
+
+import io.spine.base.EnvironmentType;
+
+/**
+ * An environment that denotes that the system is running under Google App Engine.
+ *
+ * <p>Leaves the implementation of {@link #enabled()} to subclasses.
+ */
+public abstract class AppEngine extends EnvironmentType {
+}
diff --git a/base/src/test/java/io/spine/base/given/AppEngineStandard.java b/base/src/test/java/io/spine/base/given/AppEngineStandard.java
new file mode 100644
index 0000000000..8e2aed4dc9
--- /dev/null
+++ b/base/src/test/java/io/spine/base/given/AppEngineStandard.java
@@ -0,0 +1,54 @@
+/*
+ * Copyright 2020, TeamDev. All rights reserved.
+ *
+ * Redistribution and use in source and/or binary forms, with or without
+ * modification, must retain the above copyright notice and the following
+ * disclaimer.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package io.spine.base.given;
+
+/**
+ * Determines whether the system is running under Google App Engine Standard environment.
+ */
+@SuppressWarnings("AccessOfSystemProperties")
+public class AppEngineStandard extends AppEngine {
+
+    private static final String ENV_KEY = "io.spine.base.test.is_appengine";
+
+    @Override
+    protected boolean enabled() {
+        String propertyValue = System.getProperty(ENV_KEY);
+        return activeValue().equalsIgnoreCase(propertyValue);
+    }
+
+    /**
+     * Enables the App Engine Standard environment.
+     */
+    public static void enable() {
+        System.setProperty(ENV_KEY, activeValue());
+    }
+
+    /**
+     * Disables teh App Engine Standard environment.
+     */
+    public static void clear() {
+        System.clearProperty(ENV_KEY);
+    }
+
+    private static String activeValue() {
+        return String.valueOf(true);
+    }
+}
diff --git a/license-report.md b/license-report.md
index f940bd01bc..e2e407bb25 100644
--- a/license-report.md
+++ b/license-report.md
@@ -1,6 +1,6 @@
 
     
-# Dependencies of `io.spine:spine-base:1.5.14`
+# Dependencies of `io.spine:spine-base:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -328,12 +328,12 @@
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:18:55 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:20 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-errorprone-checks:1.5.14`
+# Dependencies of `io.spine.tools:spine-errorprone-checks:1.5.15`
 
 ## Runtime
 1. **Group:** com.github.ben-manes.caffeine **Name:** caffeine **Version:** 2.7.0
@@ -773,12 +773,12 @@ This report was generated on **Sat Jun 06 13:18:55 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:18:59 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:20 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-javadoc-filter:1.5.14`
+# Dependencies of `io.spine.tools:spine-javadoc-filter:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.android **Name:** annotations **Version:** 4.1.1.4
@@ -1156,12 +1156,12 @@ This report was generated on **Sat Jun 06 13:18:59 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:01 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:21 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-javadoc-prettifier:1.5.14`
+# Dependencies of `io.spine.tools:spine-javadoc-prettifier:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -1521,12 +1521,12 @@ This report was generated on **Sat Jun 06 13:19:01 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:01 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:21 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-model-compiler:1.5.14`
+# Dependencies of `io.spine.tools:spine-model-compiler:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -1902,12 +1902,12 @@ This report was generated on **Sat Jun 06 13:19:01 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:01 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:21 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-mute-logging:1.5.14`
+# Dependencies of `io.spine.tools:spine-mute-logging:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.auto.value **Name:** auto-value-annotations **Version:** 1.6.3
@@ -2281,12 +2281,12 @@ This report was generated on **Sat Jun 06 13:19:01 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:02 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:22 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-plugin-base:1.5.14`
+# Dependencies of `io.spine.tools:spine-plugin-base:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -2646,12 +2646,12 @@ This report was generated on **Sat Jun 06 13:19:02 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:02 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:22 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-plugin-testlib:1.5.14`
+# Dependencies of `io.spine.tools:spine-plugin-testlib:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.auto.value **Name:** auto-value-annotations **Version:** 1.6.3
@@ -3065,12 +3065,12 @@ This report was generated on **Sat Jun 06 13:19:02 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:03 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:22 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-proto-dart-plugin:1.5.14`
+# Dependencies of `io.spine.tools:spine-proto-dart-plugin:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -3430,12 +3430,12 @@ This report was generated on **Sat Jun 06 13:19:03 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:03 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:23 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-proto-js-plugin:1.5.14`
+# Dependencies of `io.spine.tools:spine-proto-js-plugin:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -3795,12 +3795,12 @@ This report was generated on **Sat Jun 06 13:19:03 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:04 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:23 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-protoc-api:1.5.14`
+# Dependencies of `io.spine.tools:spine-protoc-api:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -4120,12 +4120,12 @@ This report was generated on **Sat Jun 06 13:19:04 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:04 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:23 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-protoc-plugin:1.5.14`
+# Dependencies of `io.spine.tools:spine-protoc-plugin:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -4453,12 +4453,12 @@ This report was generated on **Sat Jun 06 13:19:04 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:05 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:24 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine:spine-testlib:1.5.14`
+# Dependencies of `io.spine:spine-testlib:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.auto.value **Name:** auto-value-annotations **Version:** 1.6.3
@@ -4832,12 +4832,12 @@ This report was generated on **Sat Jun 06 13:19:05 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:05 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:24 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-tool-base:1.5.14`
+# Dependencies of `io.spine.tools:spine-tool-base:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -5165,12 +5165,12 @@ This report was generated on **Sat Jun 06 13:19:05 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:06 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Tue Jun 09 13:39:24 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
     
-# Dependencies of `io.spine.tools:spine-validation-generator:1.5.14`
+# Dependencies of `io.spine.tools:spine-validation-generator:1.5.15`
 
 ## Runtime
 1. **Group:** com.google.code.findbugs **Name:** jsr305 **Version:** 3.0.2
@@ -5498,4 +5498,4 @@ This report was generated on **Sat Jun 06 13:19:06 EEST 2020** using [Gradle-Lic
  The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
 
-This report was generated on **Sat Jun 06 13:19:06 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
\ No newline at end of file
+This report was generated on **Tue Jun 09 13:39:24 EEST 2020** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
index 8bde29d651..35f1bdbfa2 100644
--- a/pom.xml
+++ b/pom.xml
@@ -12,7 +12,7 @@ all modules and does not describe the project structure per-subproject.
 
 <groupId>io.spine</groupId>
 <artifactId>spine-base</artifactId>
-<version>1.5.14</version>
+<version>1.5.15</version>
 
 <inceptionYear>2015</inceptionYear>
 
@@ -154,7 +154,7 @@ all modules and does not describe the project structure per-subproject.
   <dependency>
     <groupId>io.spine.tools</groupId>
     <artifactId>spine-protoc-plugin</artifactId>
-    <version>1.5.14</version>
+    <version>1.5.15</version>
     <scope>test</scope>
   </dependency>
   <dependency>
diff --git a/tools/model-compiler/src/main/java/io/spine/tools/compiler/gen/column/EntityWithColumnsSpec.java b/tools/model-compiler/src/main/java/io/spine/tools/compiler/gen/column/EntityWithColumnsSpec.java
index 22716a68f2..4b47eb62c5 100644
--- a/tools/model-compiler/src/main/java/io/spine/tools/compiler/gen/column/EntityWithColumnsSpec.java
+++ b/tools/model-compiler/src/main/java/io/spine/tools/compiler/gen/column/EntityWithColumnsSpec.java
@@ -145,7 +145,7 @@ private static JavaPoetName className(FieldDeclaration declaration) {
      */
     private GeneratedJavadoc classJavadoc() {
         return GeneratedJavadoc.twoParagraph(
-                CodeBlock.of("Entity сolumns of proto type {@code $L}.", messageType.javaClassName()),
+                CodeBlock.of("Entity columns of proto type {@code $L}.", messageType.javaClassName()),
                 CodeBlock.of("Implement this type to manually override the entity column values.")
         );
     }
diff --git a/version.gradle.kts b/version.gradle.kts
index dfac331290..823a4d2e0c 100644
--- a/version.gradle.kts
+++ b/version.gradle.kts
@@ -25,7 +25,7 @@
  * as we want to manage the versions in a single source.
  */
 
-val SPINE_VERSION = "1.5.14"
+val SPINE_VERSION = "1.5.15"
 
 project.extra.apply {
     this["spineVersion"] = SPINE_VERSION