Backport addFixture() for 3.9+

src/TestSuite/TestCase.php

@@ -46,7 +46,7 @@ abstract class TestCase extends BaseTestCase
     /**
      * Fixtures used by this test case.
      *
-     * @var array|string|null
+     * @var string[]|string|null
      */
     public $fixtures;
 
@@ -914,6 +914,37 @@ abstract class TestCase extends BaseTestCase
     }
 
     /**
+     * Adds a fixture to this test case.
+     *
+     * Examples:
+     * - core.Tags
+     * - app.MyRecords
+     * - plugin.MyPluginName.MyModelName
+     *
+     * Use this method inside your test cases' {@link getFixtures()} method
+     * to build up the fixture list.
+     *
+     * @param string $fixture Fixture
+     * @return $this
+     */
+    protected function addFixture($fixture)
+    {
+        if (!isset($this->fixtures)) {
+            $this->fixtures = [];
+        } elseif (is_string($this->fixtures)) {
+            deprecationWarning(
+                'Setting fixtures as string is deprecated and will be removed in 4.0.' .
+                ' Set TestCase::$fixtures as array instead.'
+            );
+            $this->fixtures = array_map('trim', explode(',', $this->fixtures));
+        }
+
+        $this->fixtures[] = $fixture;
+
+        return $this;
+    }
+
+    /**
      * Gets fixtures.
      *
      * @return array

tests/TestCase/TestSuite/FixtureManagerTest.php

@@ -475,6 +475,7 @@ class FixtureManagerTest extends TestCase
             ->method('getFixtures')
             ->willReturn(array_keys($fixtures));
 
+        /** @var \Cake\TestSuite\Fixture\FixtureManager|\PHPUnit\Framework\MockObject\MockObject $manager */
         $manager = $this->getMockBuilder(FixtureManager::class)
             ->setMethods(['_fixtureConnections'])
             ->getMock();