Add basic test coverage for clearing out values

Spin-off issue for #2829283: Language support in Feed import

Problem/Motivation

In the latest patch from #2829283: Language support in Feed import (#54 at the time of writing) there is a method that checks for empty values (called valuesAreEmpty(). Since importing empty values is a valid use case, we need test coverage for clearing out values.

The method in question:

+++ b/src/Plugin/Type/Target/FieldTargetBase.php
@@ -76,12 +80,101 @@ abstract class FieldTargetBase extends TargetBase {
+  /**
+   * Check current field has value.
+   *
+   * This is done because we don't want set empty values to entity.
+   *
+   * @return bool
+   *   TRUE if field has value.
+   */
+  public function valuesAreEmpty(array $values) {
+    $empty = TRUE;
+    foreach ($values as $value) {
+      foreach ($value as $val) {
+        if (!empty($val)) {
+          $empty = FALSE;
+          break 2;
+        }
+      }
+    }
+    return $empty;

Proposed resolution

The D7 version of Feeds has test coverage for clearing out values for several field types. To keep work small in this issue, let's only port FeedsMapperFieldTestCase::testClearOutValues() for now.

Remaining tasks

• Port FeedsMapperFieldTestCase::testClearOutValues().

User interface changes

None.

API changes

None.

Data model changes

None.

Patch will follow.