diff -u b/src/Context/FieldResolver.php b/src/Context/FieldResolver.php
--- b/src/Context/FieldResolver.php
+++ b/src/Context/FieldResolver.php
@@ -33,4 +33,18 @@
 
   /**
+   * The entity bundle information service.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeBundleInfoInterface
+   */
+  protected $entityTypeBundleInfo;
+
+  /**
+   * The resource type repository service.
+   *
+   * @var \Drupal\jsonapi\ResourceType\ResourceTypeRepositoryInterface
+   */
+  protected $resourceTypeRepository;
+
+  /**
    * Creates a FieldResolver instance.
    *
@@ -85,7 +99,7 @@
    * resolve any aliases and/or abbreviations into a field expression that will
    * be compatible with the entity query system.
    *
-   * @see http://jsonapi.org/recommendations/#urls-reference-document
+   * @link http://jsonapi.org/recommendations/#urls-reference-document
    *
    * Example:
    *   'uid.field_first_name' -> 'uid.entity.field_first_name'.
@@ -156,7 +170,9 @@
    * Resolves the internal field name based on a collection of resource types.
    *
    * @param string $field_name
+   *   The external field name.
    * @param \Drupal\jsonapi\ResourceType\ResourceType[] $resource_types
+   *   The resource types from which to get an internal name.
    *
    * @return string
    *   The resolved internal name.
diff -u b/tests/src/Kernel/Context/FieldResolverTest.php b/tests/src/Kernel/Context/FieldResolverTest.php
--- b/tests/src/Kernel/Context/FieldResolverTest.php
+++ b/tests/src/Kernel/Context/FieldResolverTest.php
@@ -17,6 +17,8 @@
   public static $modules = ['entity_test', 'serialization', 'field', 'text'];
 
   /**
+   * The subject under test.
+   *
    * @var \Drupal\jsonapi\Context\FieldResolver
    */
   protected $sut;
@@ -81,6 +83,13 @@
   /**
    * Expects an error when an invalid field is provided.
    *
+   * @param string $entity_type
+   *   The entity type for which to test field resolution.
+   * @param string $bundle
+   *   The entity bundle for which to test field resolution.
+   * @param string $external_path
+   *   The external field path to resolve.
+   *
    * @covers ::resolveInternal
    * @dataProvider resolveInternalErrorProvider
    *
@@ -90,13 +99,17 @@
     $this->sut->resolveInternal($entity_type, $bundle, $external_path);
   }
 
+  /**
+   * Provides test cases for ::testResolveInternalError.
+   */
   public function resolveInternalErrorProvider() {
     return [
       // Should fail because none of these bundles have these fields.
       ['entity_test_with_bundle', 'bundle1', 'host.fail!!.deep'],
       ['entity_test_with_bundle', 'bundle2', 'field_test_ref2'],
       ['entity_test_with_bundle', 'bundle1', 'field_test_ref3'],
-      // Should fail because the nested field don't exist on the targeted resources.
+      // Should fail because the nested fields don't exist on the targeted
+      // resource types.
       ['entity_test_with_bundle', 'bundle1', 'field_test_ref1.field_test1'],
       ['entity_test_with_bundle', 'bundle1', 'field_test_ref1.field_test2'],
       ['entity_test_with_bundle', 'bundle1', 'field_test_ref1.field_test_ref1'],
@@ -106,6 +119,9 @@
 
   /**
    * Create a simple bundle.
+   *
+   * @param string $name
+   *   The name of the bundle to create.
    */
   protected function makeBundle($name) {
     EntityTestBundle::create([
@@ -113,7 +129,23 @@
     ])->save();
   }
 
-  protected function makeField($type, $name, $entity_type, $bundles, $storage_settings = [], $config_settings = []) {
+  /**
+   * Creates a field for a specified entity type/bundle.
+   *
+   * @param string $type
+   *   The field type.
+   * @param string $name
+   *   The name of the field to create.
+   * @param string $entity_type
+   *   The entity type to which the field will be attached.
+   * @param string[] $bundles
+   *   The entity bundles to which the field will be attached.
+   * @param array $storage_settings
+   *   Custom storage settings for the field.
+   * @param array $config_settings
+   *   Custom configuration settings for the field.
+   */
+  protected function makeField($type, $name, $entity_type, array $bundles, array $storage_settings = [], array $config_settings = []) {
     $storage_config = [
       'field_name' => $name,
       'type' => $type,