Add dist test

core/src/main/java/org/mapfish/print/test/util/ImageSimilarity.java

@@ -216,7 +216,7 @@ private File getRelatedFile(final String name) {
    *
    * @return a number between 0 and 10000 or Double.MAX_VALUE on images format error.
    */
-  private double calcDistance(final BufferedImage actual) {
+  protected double calcDistance(final BufferedImage actual) {
     // There are several ways to calculate distances between two vectors,
     // we will calculate the sum of the distances between the RGB values of
     // pixels in the same positions.

core/src/test/java/org/mapfish/print/test/util/ImageSimilarityTest.java

@@ -0,0 +1,25 @@
+package org.mapfish.print;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import javax.imageio.ImageIO;
+import org.junit.Test;
+import org.mapfish.print.test.util.ImageSimilarity;
+
+public class ImageSimilarityTest extends AbstractMapfishSpringTest {
+
+  @Test
+  public void testRegenerateFalse() throws Exception {
+    assertFalse(
+        "This flag should not be committed as true", ImageSimilarity.REGENERATE_EXPECTED_IMAGES);
+  }
+
+  @Test
+  public void testDist() throws Exception {
+    assertTrue(
+        new ImageSimilarity(getFile("imageSimilarity/with.png"))
+                .calcDistance(ImageIO.read(getFile("imageSimilarity/without.png")))
+            > 0);
+  }
+}