diff --git a/modules/backend/ServiceProvider.php b/modules/backend/ServiceProvider.php
index 839f81d808..bc0708e6d5 100644
--- a/modules/backend/ServiceProvider.php
+++ b/modules/backend/ServiceProvider.php
@@ -1,6 +1,5 @@
 <?php namespace Backend;
 
-use App;
 use Backend;
 use BackendMenu;
 use BackendAuth;
@@ -23,12 +22,15 @@ public function register()
         $this->registerConsole();
         $this->registerMailer();
         $this->registerAssetBundles();
-        $this->registerBackendPermissions();
+
+        if (!$this->app->runningUnitTests()) {
+            $this->registerBackendPermissions();
+        }
 
         /*
          * Backend specific
          */
-        if (App::runningInBackend()) {
+        if ($this->app->runningInBackend()) {
             $this->registerBackendNavigation();
             $this->registerBackendReportWidgets();
             $this->registerBackendWidgets();
diff --git a/modules/backend/behaviors/FormController.php b/modules/backend/behaviors/FormController.php
index 25660de317..ae58bb475f 100644
--- a/modules/backend/behaviors/FormController.php
+++ b/modules/backend/behaviors/FormController.php
@@ -177,7 +177,7 @@ public function initForm($model, $context = null)
          * Detected Relation controller behavior
          */
         if ($this->controller->isClassExtendedWith(\Backend\Behaviors\RelationController::class)) {
-            $this->controller->initRelation($model);
+            $this->controller->initRelation(clone $model);
         }
 
         $this->prepareVars($model);
diff --git a/modules/backend/formwidgets/FileUpload.php b/modules/backend/formwidgets/FileUpload.php
index ae401ad6f4..dc92668304 100644
--- a/modules/backend/formwidgets/FileUpload.php
+++ b/modules/backend/formwidgets/FileUpload.php
@@ -173,7 +173,7 @@ protected function getFileRecord()
         $record = false;
 
         if (!empty(post('file_id'))) {
-            $record = $this->getRelationModel()::find(post('file_id')) ?: false;
+            $record = $this->getRelationModel()->find(post('file_id')) ?: false;
         }
 
         return $record;
@@ -181,10 +181,8 @@ protected function getFileRecord()
 
     /**
      * Get the instantiated config Form widget
-     *
-     * @return void
      */
-    public function getConfigFormWidget()
+    public function getConfigFormWidget(): Form
     {
         if ($this->configFormWidget) {
             return $this->configFormWidget;
@@ -222,9 +220,8 @@ protected function getFileList()
 
     /**
      * Returns the display mode for the file upload. Eg: file-multi, image-single, etc.
-     * @return string
      */
-    protected function getDisplayMode()
+    protected function getDisplayMode(): string
     {
         $mode = $this->getConfig('mode', 'image');
 
@@ -233,16 +230,15 @@ protected function getDisplayMode()
         }
 
         $relationType = $this->getRelationType();
-        $mode .= ($relationType == 'attachMany' || $relationType == 'morphMany') ? '-multi' : '-single';
+        $mode .= ($relationType === 'attachMany' || $relationType === 'morphMany') ? '-multi' : '-single';
 
         return $mode;
     }
 
     /**
      * Returns the escaped and translated prompt text to display according to the type.
-     * @return string
      */
-    protected function getPromptText()
+    protected function getPromptText(): string
     {
         if ($this->prompt === null) {
             $isMulti = ends_with($this->getDisplayMode(), 'multi');
@@ -257,10 +253,8 @@ protected function getPromptText()
     /**
      * Returns the CSS dimensions for the uploaded image,
      * uses auto where no dimension is provided.
-     * @param string $mode
-     * @return string
      */
-    protected function getCssDimensions($mode = null)
+    protected function getCssDimensions(?string $mode = null): string
     {
         if (!$this->imageWidth && !$this->imageHeight) {
             return '';
@@ -270,20 +264,19 @@ protected function getCssDimensions($mode = null)
 
         if ($mode == 'block') {
             $cssDimensions .= $this->imageWidth
-                ? 'width: '.$this->imageWidth.'px;'
-                : 'width: '.$this->imageHeight.'px;';
+                ? 'width: ' . $this->imageWidth . 'px;'
+                : 'width: ' . $this->imageHeight . 'px;';
 
             $cssDimensions .= ($this->imageHeight)
-                ? 'max-height: '.$this->imageHeight.'px;'
+                ? 'max-height: ' . $this->imageHeight . 'px;'
                 : 'height: auto;';
-        }
-        else {
+        } else {
             $cssDimensions .= $this->imageWidth
-                ? 'width: '.$this->imageWidth.'px;'
+                ? 'width: ' . $this->imageWidth . 'px;'
                 : 'width: auto;';
 
             $cssDimensions .= ($this->imageHeight)
-                ? 'max-height: '.$this->imageHeight.'px;'
+                ? 'max-height: ' . $this->imageHeight . 'px;'
                 : 'height: auto;';
         }
 
@@ -333,18 +326,19 @@ public function getAcceptedFileTypes($includeDot = false)
     /**
      * Removes a file attachment.
      */
-    public function onRemoveAttachment()
+    public function onRemoveAttachment(): void
     {
-        $fileModel = $this->getRelationModel();
-        if (($fileId = post('file_id')) && ($file = $fileModel::find($fileId))) {
+        if ($file = $this->getFileRecord()) {
             $this->getRelationObject()->remove($file, $this->sessionKey);
         }
     }
 
     /**
      * Sorts file attachments.
+     *
+     * Expects (array) sortOrder [$fileId => $fileOrder] in the POST data.
      */
-    public function onSortAttachments()
+    public function onSortAttachments(): void
     {
         if ($sortData = post('sortOrder')) {
             $ids = array_keys($sortData);
@@ -357,10 +351,11 @@ public function onSortAttachments()
 
     /**
      * Loads the configuration form for an attachment, allowing title and description to be set.
+     *
+     * @throws ApplicationException if unable to find the file record
      */
-    public function onLoadAttachmentConfig()
+    public function onLoadAttachmentConfig(): string
     {
-        $fileModel = $this->getRelationModel();
         if ($file = $this->getFileRecord()) {
             $file = $this->decorateFileAttributes($file);
 
diff --git a/modules/backend/formwidgets/RecordFinder.php b/modules/backend/formwidgets/RecordFinder.php
index 3ea6522c68..982e12dc01 100644
--- a/modules/backend/formwidgets/RecordFinder.php
+++ b/modules/backend/formwidgets/RecordFinder.php
@@ -3,6 +3,7 @@
 use Lang;
 use ApplicationException;
 use Backend\Classes\FormWidgetBase;
+use Winter\Storm\Database\Model;
 
 /**
  * Record Finder
@@ -312,10 +313,8 @@ public function onFindRecord()
 
     /**
      * Gets the base model instance used by this field
-     *
-     * @return \Winter\Storm\Database\Model
      */
-    protected function getRecordModel()
+    protected function getRecordModel(): Model
     {
         $model = null;
         if ($this->useRelation) {
diff --git a/modules/backend/formwidgets/TagList.php b/modules/backend/formwidgets/TagList.php
index 0bdc0c13c4..8389654108 100644
--- a/modules/backend/formwidgets/TagList.php
+++ b/modules/backend/formwidgets/TagList.php
@@ -120,9 +120,8 @@ public function getSaveValue($value)
     /**
      * Returns an array suitable for saving against a relation (array of keys).
      * This method also creates non-existent tags.
-     * @return array
      */
-    protected function hydrateRelationSaveValue($names)
+    protected function hydrateRelationSaveValue($names): array
     {
         if (!$names) {
             return $names;
diff --git a/modules/backend/traits/FormModelWidget.php b/modules/backend/traits/FormModelWidget.php
index 5da7cc1d90..23215c4bef 100644
--- a/modules/backend/traits/FormModelWidget.php
+++ b/modules/backend/traits/FormModelWidget.php
@@ -3,6 +3,8 @@
 use Lang;
 use ApplicationException;
 use Exception;
+use Winter\Storm\Database\Model;
+use Winter\Storm\Database\Relations\Relation;
 
 /**
  * Form Model Widget Trait
@@ -12,18 +14,14 @@
  * @package winter\wn-backend-module
  * @author Alexey Bobkov, Samuel Georges
  */
-
 trait FormModelWidget
 {
-
     /**
-     * Returns the final model and attribute name of
-     * a nested HTML array attribute.
+     * Returns the final model and attribute name of a nested HTML array attribute.
      * Eg: list($model, $attribute) = $this->resolveModelAttribute($this->valueFrom);
-     * @param  string $attribute.
-     * @return array
+     * @throws ApplicationException if something goes wrong when attempting to resolve the model attribute
      */
-    public function resolveModelAttribute($attribute)
+    public function resolveModelAttribute(string $attribute): array
     {
         try {
             return $this->formField->resolveModelAttribute($this->model, $attribute);
@@ -37,11 +35,10 @@ public function resolveModelAttribute($attribute)
     }
 
     /**
-     * Returns the model of a relation type,
-     * supports nesting via HTML array.
-     * @return Relation
+     * Returns the model of a relation type, supports nesting via HTML array.
+     * @throws ApplicationException if the related model cannot be resolved
      */
-    public function getRelationModel()
+    public function getRelationModel(): Model
     {
         list($model, $attribute) = $this->resolveModelAttribute($this->valueFrom);
 
@@ -63,11 +60,10 @@ public function getRelationModel()
     }
 
     /**
-     * Returns the value as a relation object from the model,
-     * supports nesting via HTML array.
-     * @return Relation
+     * Returns the value as a relation object from the model, supports nesting via HTML array.
+     * @throws ApplicationException if the relationship cannot be resolved
      */
-    protected function getRelationObject()
+    protected function getRelationObject(): Relation
     {
         list($model, $attribute) = $this->resolveModelAttribute($this->valueFrom);
 
@@ -89,11 +85,9 @@ protected function getRelationObject()
     }
 
     /**
-     * Returns the value as a relation type from the model,
-     * supports nesting via HTML array.
-     * @return Relation
+     * Returns the value as a relation type from the model, supports nesting via HTML array.
      */
-    protected function getRelationType()
+    protected function getRelationType(): ?string
     {
         list($model, $attribute) = $this->resolveModelAttribute($this->valueFrom);
         return $model->getRelationType($attribute);
diff --git a/modules/backend/widgets/Lists.php b/modules/backend/widgets/Lists.php
index dc9e181254..c0837e2885 100644
--- a/modules/backend/widgets/Lists.php
+++ b/modules/backend/widgets/Lists.php
@@ -1802,11 +1802,10 @@ public function onToggleTreeNode()
 
     /**
      * Check if column refers to a relation of the model
-     * @param  ListColumn  $column List column object
      * @param  boolean     $multi  If set, returns true only if the relation is a "multiple relation type"
      * @return boolean
      */
-    protected function isColumnRelated($column, $multi = false)
+    protected function isColumnRelated(ListColumn $column, bool $multi = false): bool
     {
         if (!isset($column->relation) || $this->isColumnPivot($column)) {
             return false;
diff --git a/modules/cms/ServiceProvider.php b/modules/cms/ServiceProvider.php
index ae901c4a94..2398e6f476 100644
--- a/modules/cms/ServiceProvider.php
+++ b/modules/cms/ServiceProvider.php
@@ -1,30 +1,28 @@
 <?php namespace Cms;
 
-use App;
-use Url;
-use Lang;
-use File;
-use Event;
-use Config;
 use Backend;
-use BackendMenu;
+use Backend\Classes\WidgetManager;
+use Backend\Models\UserRole;
 use BackendAuth;
-use Cms\Models\ThemeLog;
-use Cms\Models\ThemeData;
+use BackendMenu;
 use Cms\Classes\CmsObject;
-use Backend\Models\UserRole;
-use Cms\Classes\Page as CmsPage;
 use Cms\Classes\ComponentManager;
+use Cms\Classes\Page as CmsPage;
+use Cms\Classes\Theme;
+use Cms\Models\ThemeData;
+use Cms\Models\ThemeLog;
+use Cms\Twig\DebugExtension;
+use Cms\Twig\Extension as CmsTwigExtension;
+use Cms\Twig\Loader as CmsTwigLoader;
+use Config;
+use Event;
+use File;
+use Lang;
 use System\Classes\CombineAssets;
-use Cms\Classes\Theme as CmsTheme;
-use Backend\Classes\WidgetManager;
 use System\Classes\MarkupManager;
 use System\Classes\SettingsManager;
 use Twig\Cache\FilesystemCache as TwigCacheFilesystem;
-use Cms\Twig\Loader as CmsTwigLoader;
-use Cms\Twig\DebugExtension;
-use Cms\Twig\Extension as CmsTwigExtension;
-
+use Url;
 use Winter\Storm\Support\ModuleServiceProvider;
 
 class ServiceProvider extends ModuleServiceProvider
@@ -43,12 +41,15 @@ public function register()
         $this->registerThemeLogging();
         $this->registerCombinerEvents();
         $this->registerHalcyonModels();
-        $this->registerBackendPermissions();
+
+        if (!$this->app->runningUnitTests()) {
+            $this->registerBackendPermissions();
+        }
 
         /*
          * Backend specific
          */
-        if (App::runningInBackend()) {
+        if ($this->app->runningInBackend()) {
             $this->registerBackendNavigation();
             $this->registerBackendReportWidgets();
             $this->registerBackendWidgets();
@@ -68,7 +69,7 @@ public function boot()
         $this->bootMenuItemEvents();
         $this->bootRichEditorEvents();
 
-        if (App::runningInBackend()) {
+        if ($this->app->runningInBackend()) {
             $this->bootBackendLocalization();
         }
     }
@@ -94,7 +95,7 @@ protected function registerConsole()
     protected function registerTwigParser()
     {
         // Register CMS Twig environment
-        App::bind('twig.environment.cms', function ($app) {
+        $this->app->bind('twig.environment.cms', function ($app) {
             // Load Twig options
             $useCache = !Config::get('cms.twigNoCache');
             $isDebugMode = Config::get('app.debug', false);
@@ -163,7 +164,7 @@ protected function registerThemeLogging()
      */
     protected function registerCombinerEvents()
     {
-        if (App::runningInBackend() || App::runningInConsole()) {
+        if ($this->app->runningInBackend() || $this->app->runningInConsole()) {
             return;
         }
 
@@ -386,7 +387,7 @@ protected function registerBackendSettings()
      */
     protected function bootBackendLocalization()
     {
-        $theme = CmsTheme::getActiveTheme();
+        $theme = Theme::getActiveTheme();
 
         if (is_null($theme)) {
             return;
diff --git a/modules/system/ServiceProvider.php b/modules/system/ServiceProvider.php
index 0d2a4118f1..6027d8fd31 100644
--- a/modules/system/ServiceProvider.php
+++ b/modules/system/ServiceProvider.php
@@ -1,33 +1,30 @@
 <?php namespace System;
 
-use Db;
-use App;
-use View;
-use Event;
-use Config;
 use Backend;
-use Request;
-use Validator;
-use BackendMenu;
-use BackendAuth;
-use SystemException;
+use Backend\Classes\WidgetManager;
 use Backend\Models\UserRole;
-use System\Classes\MailManager;
+use BackendAuth;
+use BackendMenu;
+use Config;
+use Event;
+use Illuminate\Pagination\Paginator;
+use Illuminate\Support\Facades\Schema;
+use Request;
+use System\Classes\CombineAssets;
 use System\Classes\ErrorHandler;
+use System\Classes\MailManager;
 use System\Classes\MarkupManager;
 use System\Classes\PluginManager;
 use System\Classes\SettingsManager;
 use System\Classes\UpdateManager;
-use System\Twig\Engine as TwigEngine;
 use System\Models\EventLog;
 use System\Models\MailSetting;
-use System\Classes\CombineAssets;
-use Backend\Classes\WidgetManager;
-use Winter\Storm\Support\ModuleServiceProvider;
+use System\Twig\Engine as TwigEngine;
+use SystemException;
+use Validator;
+use View;
 use Winter\Storm\Router\Helper as RouterHelper;
-use Illuminate\Pagination\Paginator;
-use Illuminate\Support\Facades\Schema;
-use System\Classes\MixAssets;
+use Winter\Storm\Support\ModuleServiceProvider;
 
 class ServiceProvider extends ModuleServiceProvider
 {
@@ -61,16 +58,18 @@ public function register()
          */
         foreach (Config::get('cms.loadModules', []) as $module) {
             if (strtolower(trim($module)) != 'system') {
-                App::register('\\' . $module . '\ServiceProvider');
+                $this->app->register('\\' . $module . '\ServiceProvider');
             }
         }
 
-        $this->registerBackendPermissions();
+        if (!$this->app->runningUnitTests()) {
+            $this->registerBackendPermissions();
+        }
 
         /*
          * Backend specific
          */
-        if (App::runningInBackend()) {
+        if ($this->app->runningInBackend()) {
             $this->registerBackendNavigation();
             $this->registerBackendReportWidgets();
             $this->registerBackendSettings();
@@ -114,19 +113,19 @@ public function boot()
      */
     protected function registerSingletons()
     {
-        App::singleton('cms.helper', function () {
+        $this->app->singleton('cms.helper', function () {
             return new \Cms\Helpers\Cms;
         });
 
-        App::singleton('backend.helper', function () {
+        $this->app->singleton('backend.helper', function () {
             return new \Backend\Helpers\Backend;
         });
 
-        App::singleton('backend.menu', function () {
+        $this->app->singleton('backend.menu', function () {
             return \Backend\Classes\NavigationManager::instance();
         });
 
-        App::singleton('backend.auth', function () {
+        $this->app->singleton('backend.auth', function () {
             return \Backend\Classes\AuthManager::instance();
         });
     }
@@ -157,7 +156,7 @@ protected function registerPrivilegedActions()
         /*
          * CLI
          */
-        if (App::runningInConsole() && count(array_intersect($commands, Request::server('argv', []))) > 0) {
+        if ($this->app->runningInConsole() && count(array_intersect($commands, Request::server('argv', []))) > 0) {
             PluginManager::$noInit = true;
         }
     }
@@ -221,7 +220,7 @@ protected function registerConsole()
          */
         Event::listen('console.schedule', function ($schedule) {
             // Fix initial system migration with plugins that use settings for scheduling - see #3208
-            if (App::hasDatabase() && !Schema::hasTable(UpdateManager::instance()->getMigrationTableName())) {
+            if ($this->app->hasDatabase() && !Schema::hasTable(UpdateManager::instance()->getMigrationTableName())) {
                 return;
             }
 
@@ -307,20 +306,20 @@ protected function registerLogging()
     protected function registerTwigParser()
     {
         // Register System Twig environment
-        App::singleton('twig.environment', function ($app) {
+        $this->app->singleton('twig.environment', function ($app) {
             return MarkupManager::makeBaseTwigEnvironment();
         });
 
         // Register Mailer Twig environment
-        App::singleton('twig.environment.mailer', function ($app) {
+        $this->app->singleton('twig.environment.mailer', function ($app) {
             $twig = MarkupManager::makeBaseTwigEnvironment();
             $twig->addTokenParser(new \System\Twig\MailPartialTokenParser);
             return $twig;
         });
 
         // Register .htm extension for Twig views
-        App::make('view')->addExtension('htm', 'twig', function () {
-            return new TwigEngine(App::make('twig.environment'));
+        $this->app->make('view')->addExtension('htm', 'twig', function () {
+            return new TwigEngine($this->app->make('twig.environment'));
         });
     }