diff --git a/src/updater.h b/src/updater.h
index 0a9cf782..01de5d5d 100644
--- a/src/updater.h
+++ b/src/updater.h
@@ -35,16 +35,24 @@ class Configuration;
 class MetadataUpdater {
  public:
   struct ResourceMetadata {
-    ResourceMetadata(const std::vector<std::string>& ids_,
-                     const MonitoredResource& resource_,
-                     MetadataStore::Metadata&& metadata_)
-        : ids(ids_), resource(resource_), metadata(std::move(metadata_)) {}
+    ResourceMetadata(const std::vector<std::string>& ids,
+                     const MonitoredResource& resource,
+                     MetadataStore::Metadata&& metadata)
+        : ids_(ids), resource_(resource), metadata_(std::move(metadata)) {}
     ResourceMetadata(ResourceMetadata&& other)
-        : ResourceMetadata(other.ids, other.resource,
-                           std::move(other.metadata)) {}
-    std::vector<std::string> ids;
-    MonitoredResource resource;
-    MetadataStore::Metadata metadata;
+        : ResourceMetadata(other.ids_, other.resource_,
+                           std::move(other.metadata_)) {}
+
+    const MetadataStore::Metadata& metadata() const { return metadata_; }
+    const MonitoredResource& resource() const { return resource_; }
+    const std::vector<std::string>& ids() const { return ids_; }
+
+   private:
+    friend class MetadataUpdater;  // Needs write access to metadata_.
+
+    std::vector<std::string> ids_;
+    MonitoredResource resource_;
+    MetadataStore::Metadata metadata_;
   };
 
   MetadataUpdater(const Configuration& config, MetadataStore* store,
@@ -75,12 +83,12 @@ class MetadataUpdater {
 
   // Updates the resource map in the store.
   void UpdateResourceCallback(const ResourceMetadata& result) {
-    store_->UpdateResource(result.ids, result.resource);
+    store_->UpdateResource(result.ids_, result.resource_);
   }
 
   // Updates the metadata in the store. Consumes result.
   void UpdateMetadataCallback(ResourceMetadata&& result) {
-    store_->UpdateMetadata(result.resource, std::move(result.metadata));
+    store_->UpdateMetadata(result.resource_, std::move(result.metadata_));
   }
 
   const Configuration& config() {
@@ -112,6 +120,8 @@ class PollingMetadataUpdater : public MetadataUpdater {
   void StopUpdater();
 
  private:
+  friend class InstanceTest;
+
   // Metadata poller.
   void PollForMetadata();
 
diff --git a/test/Makefile b/test/Makefile
index 08ace465..30f3b9df 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -44,6 +44,7 @@ TESTS=\
       configuration_unittest \
       format_unittest \
       health_checker_unittest \
+      instance_unittest \
       json_unittest \
       kubernetes_unittest \
       resource_unittest \
@@ -104,6 +105,12 @@ base64_unittest: base64_unittest.o $(SRC_DIR)/base64.o
 	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
 configuration_unittest: configuration_unittest.o $(SRC_DIR)/configuration.o
 	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
+health_checker_unittest: health_checker_unittest.o $(SRC_DIR)/health_checker.o $(SRC_DIR)/configuration.o
+	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -lboost_filesystem -lboost_system -o $@
+instance_unittest: instance_unittest.o $(SRC_DIR)/instance.o $(SRC_DIR)/configuration.o $(SRC_DIR)/environment.o $(SRC_DIR)/format.o $(SRC_DIR)/json.o $(SRC_DIR)/logging.o $(SRC_DIR)/resource.o $(SRC_DIR)/store.o $(SRC_DIR)/time.o
+	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
+json_unittest: json_unittest.o $(SRC_DIR)/json.o
+	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
 kubernetes_unittest: kubernetes_unittest.o $(SRC_DIR)/kubernetes.o $(SRC_DIR)/json.o $(SRC_DIR)/logging.o $(SRC_DIR)/environment.o $(SRC_DIR)/time.o $(SRC_DIR)/store.o $(SRC_DIR)/resource.o $(SRC_DIR)/updater.o $(SRC_DIR)/instance.o $(SRC_DIR)/format.o $(SRC_DIR)/configuration.o $(SRC_DIR)/health_checker.o
 	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
 resource_unittest: resource_unittest.o $(SRC_DIR)/resource.o $(SRC_DIR)/json.o
@@ -112,9 +119,5 @@ store_unittest: store_unittest.o $(SRC_DIR)/store.o $(SRC_DIR)/resource.o $(SRC_
 	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
 time_unittest: time_unittest.o $(SRC_DIR)/time.o
 	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
-health_checker_unittest: health_checker_unittest.o $(SRC_DIR)/health_checker.o $(SRC_DIR)/configuration.o
-	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -lboost_filesystem -lboost_system -o $@
-json_unittest: json_unittest.o $(SRC_DIR)/json.o
-	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
 
 .PHONY: all test clean purge
diff --git a/test/instance_unittest.cc b/test/instance_unittest.cc
new file mode 100644
index 00000000..b6534f79
--- /dev/null
+++ b/test/instance_unittest.cc
@@ -0,0 +1,45 @@
+#include "../src/configuration.h"
+#include "../src/environment.h"
+#include "../src/instance.h"
+#include "../src/resource.h"
+#include "../src/updater.h"
+#include "gtest/gtest.h"
+
+namespace google {
+
+namespace {
+
+TEST(InstanceTest, GetInstanceMonitoredResource) {
+  Configuration config(std::istringstream(
+      "InstanceResourceType: gce_instance\n"
+      "InstanceId: 1234567891011\n"
+      "InstanceZone: us-east1-b\n"
+  ));
+  Environment env(config);
+  EXPECT_EQ(MonitoredResource("gce_instance", {
+    {"instance_id", "1234567891011"},
+    {"zone", "us-east1-b"}
+  }), InstanceReader::InstanceResource(env));
+}
+
+TEST(InstanceTest, GetInstanceMetatadataQuery) {
+  Configuration config(std::istringstream(
+      "InstanceResourceType: gce_instance\n"
+      "InstanceId: 1234567891011\n"
+      "InstanceZone: us-east1-b\n"
+  ));
+  InstanceReader reader(config);
+  const auto result = reader.MetadataQuery();
+  EXPECT_EQ(1, result.size());
+  const MetadataUpdater::ResourceMetadata& rm = result[0];
+  EXPECT_EQ(MonitoredResource("gce_instance", {
+    {"instance_id", "1234567891011"},
+    {"zone", "us-east1-b"}
+  }), rm.resource());
+  EXPECT_EQ(std::vector<std::string>({"", "1234567891011"}), rm.ids());
+  EXPECT_TRUE(rm.metadata().ignore);
+}
+
+}  // namespace
+
+}  // google
diff --git a/test/kubernetes_unittest.cc b/test/kubernetes_unittest.cc
index 79e4ac94..455c2b10 100644
--- a/test/kubernetes_unittest.cc
+++ b/test/kubernetes_unittest.cc
@@ -34,18 +34,18 @@ TEST_F(KubernetesTest, GetNodeMetadata) {
   });
   const auto m =
       GetNodeMetadata(reader, node->As<json::Object>(), Timestamp(), false);
-  EXPECT_EQ(1, m.ids.size());
-  EXPECT_EQ("k8s_node.testname", m.ids[0]);
+  EXPECT_EQ(1, m.ids().size());
+  EXPECT_EQ("k8s_node.testname", m.ids()[0]);
   EXPECT_EQ(MonitoredResource("k8s_node", {
     {"cluster_name", "TestClusterName"},
     {"node_name", "testname"},
     {"location", "TestClusterLocation"},
-  }), m.resource);
-  EXPECT_EQ("TestVersion", m.metadata.version);
-  EXPECT_EQ(false, m.metadata.is_deleted);
+  }), m.resource());
+  EXPECT_EQ("TestVersion", m.metadata().version);
+  EXPECT_EQ(false, m.metadata().is_deleted);
   EXPECT_EQ(time::rfc3339::FromString("2018-03-03T01:23:45.678901234Z"),
-            m.metadata.created_at);
-  EXPECT_EQ(Timestamp(), m.metadata.collected_at);
+            m.metadata().created_at);
+  EXPECT_EQ(Timestamp(), m.metadata().collected_at);
   json::value big = json::object({
     {"blobs", json::object({
       {"association", json::object({
@@ -66,6 +66,6 @@ TEST_F(KubernetesTest, GetNodeMetadata) {
       })},
     })},
   });
-  EXPECT_EQ(big->ToString(), m.metadata.metadata->ToString());
+  EXPECT_EQ(big->ToString(), m.metadata().metadata->ToString());
 }
 }  // namespace google