Add integration test for watermark with alpha

Added integration tests for handling alpha transparency in watermarks.
Renamed the current test for watermarks as it only tests if the
watermark is correctly places

dev/tests/integration/testsuite/Magento/Framework/Image/Adapter/InterfaceTest.php

@@ -337,6 +337,97 @@ public function rotateDataProvider()
         );
     }
 
+    /**
+     * Test if alpha transparency is correctly handled
+     *
+     * @param string $image
+     * @param string $watermark
+     * @param int $alphaPercentage
+     * @param array $comparePoint1
+     * @param array $comparePoint2
+     * @param string $adapterType
+     *
+     * @dataProvider imageWatermarkWithAlphaTransparencyDataProvider
+     * @depends testOpen
+     * @depends testImageSize
+     */
+    public function testWatermarkWithAlphaTransparency(
+        $image,
+        $watermark,
+        $alphaPercentage,
+        $comparePoint1,
+        $comparePoint2,
+        $adapterType
+    ) {
+        $imageAdapter = $this->_getAdapter($adapterType);
+        $imageAdapter->open($image);
+
+        $watermarkAdapter = $this->_getAdapter($adapterType);
+        $watermarkAdapter->open($watermark);
+
+        list($comparePoint1X, $comparePoint1Y) = $comparePoint1;
+        list($comparePoint2X, $comparePoint2Y) = $comparePoint2;
+
+        $imageAdapter
+            ->setWatermarkImageOpacity($alphaPercentage)
+            ->setWatermarkPosition(\Magento\Framework\Image\Adapter\AbstractAdapter::POSITION_TOP_LEFT)
+            ->watermark($watermark);
+
+        $comparePoint1Color = $imageAdapter->getColorAt($comparePoint1X, $comparePoint1Y);
+        unset($comparePoint1Color['alpha']);
+
+        $comparePoint2Color = $imageAdapter->getColorAt($comparePoint2X, $comparePoint2Y);
+        unset($comparePoint2Color['alpha']);
+
+        $result = $this->_compareColors($comparePoint1Color, $comparePoint2Color);
+        $message = sprintf(
+            '%s should be different to %s due to alpha transparency',
+            join(',', $comparePoint1Color),
+            join(',', $comparePoint2Color)
+        );
+        $this->assertFalse($result, $message);
+    }
+
+    public function imageWatermarkWithAlphaTransparencyDataProvider()
+    {
+        return $this->_prepareData(
+            [
+                // Watermark with alpha channel, 25%
+                [
+                    $this->_getFixture('watermark_alpha_base_image.jpg'),
+                    $this->_getFixture('watermark_alpha.png'),
+                    25,
+                    [ 23, 3 ],
+                    [ 23, 30 ]
+                ],
+                // Watermark with alpha channel, 50%
+                [
+                    $this->_getFixture('watermark_alpha_base_image.jpg'),
+                    $this->_getFixture('watermark_alpha.png'),
+                    50,
+                    [ 23, 3 ],
+                    [ 23, 30 ]
+                ],
+                // Watermark with no alpha channel, 50%
+                [
+                    $this->_getFixture('watermark_alpha_base_image.jpg'),
+                    $this->_getFixture('watermark.png'),
+                    50,
+                    [ 3, 3 ],
+                    [ 23,3 ]
+                ],
+                // Watermark with no alpha channel, 100%
+                [
+                    $this->_getFixture('watermark_alpha_base_image.jpg'),
+                    $this->_getFixture('watermark.png'),
+                    100,
+                    [ 3, 3 ],
+                    [ 3, 60 ]
+                ],
+            ]
+        );
+    }
+
     /**
      * Checks if watermark exists on the right position
      *
@@ -350,10 +441,10 @@ public function rotateDataProvider()
      * @param int $colorY
      * @param string $adapterType
      *
-     * @dataProvider imageWatermarkDataProvider
+     * @dataProvider imageWatermarkPositionDataProvider
      * @depends testOpen
      */
-    public function testWatermark(
+    public function testWatermarkPosition(
         $image,
         $watermark,
         $width,
@@ -387,7 +478,7 @@ public function testWatermark(
         $this->assertFalse($result, $message);
     }
 
-    public function imageWatermarkDataProvider()
+    public function imageWatermarkPositionDataProvider()
     {
         return $this->_prepareData(
             [