diff --git a/tests/phpunit/MediaWikiTestCase.php b/tests/phpunit/MediaWikiTestCase.php
index c619dab805e..99c96f29167 100644
--- a/tests/phpunit/MediaWikiTestCase.php
+++ b/tests/phpunit/MediaWikiTestCase.php
@@ -789,4 +789,24 @@ abstract class MediaWikiTestCase extends PHPUnit_Framework_TestCase {
 		//        But frequently, this is used in fixture setup.
 		throw new MWException( "No namespace defaults to wikitext!" );
 	}
+
+	/**
+	 * Check, if $wgDiff3 is set and ready to merge
+	 * Will mark the calling test as skipped, if not ready
+	 *
+	 * @since 1.21
+	 */
+	protected function checkHasDiff3() {
+		global $wgDiff3;
+
+		# This check may also protect against code injection in
+		# case of broken installations.
+		wfSuppressWarnings();
+		$haveDiff3 = $wgDiff3 && file_exists( $wgDiff3 );
+		wfRestoreWarnings();
+
+		if( !$haveDiff3 ) {
+			$this->markTestSkipped( "Skip test, since diff3 is not configured" );
+		}
+	}
 }
diff --git a/tests/phpunit/includes/EditPageTest.php b/tests/phpunit/includes/EditPageTest.php
index b02b08a3cb9..36fde854d7c 100644
--- a/tests/phpunit/includes/EditPageTest.php
+++ b/tests/phpunit/includes/EditPageTest.php
@@ -356,25 +356,13 @@ hello
 		return array_merge( $tests, $testsWithAdam, $testsWithBerta );
 	}
 
-	function testHasValidDiff3() {
-		global $wgDiff3;
-
-		if ( !$wgDiff3 ) {
-			$this->markTestSkipped( "Can't test conflict resolution because \$wgDiff3 is not configured" );
-		} elseif ( !file_exists( $wgDiff3 ) ) {
-			#XXX: this sucks, since it uses arcane internal knowledge about TextContentHandler::merge3 and wfMerge.
-			$this->markTestSkipped( "Can't test conflict resolution because \$wgDiff3 is misconfigured: can't find $wgDiff3" );
-		}
-		$this->assertTrue( true );
-	}
-
 	/**
-	 * @depend testHasValidDiff3
 	 * @dataProvider provideAutoMerge
 	 */
 	public function testAutoMerge( $baseUser, $text, $adamsEdit, $bertasEdit,
 				$expectedCode, $expectedText, $message = null
 	) {
+		$this->checkHasDiff3();
 
 		//create page
 		$ns = $this->getDefaultWikitextNS();
diff --git a/tests/phpunit/includes/GlobalFunctions/GlobalTest.php b/tests/phpunit/includes/GlobalFunctions/GlobalTest.php
index 7304bd95510..0dc18a2919b 100644
--- a/tests/phpunit/includes/GlobalFunctions/GlobalTest.php
+++ b/tests/phpunit/includes/GlobalFunctions/GlobalTest.php
@@ -498,6 +498,8 @@ class GlobalTest extends MediaWikiTestCase {
 	 * @dataProvider provideMerge()
 	 */
 	public function testMerge( $old, $mine, $yours, $expectedMergeResult, $expectedText ) {
+		$this->checkHasDiff3();
+
 		$mergedText = null;
 		$isMerged = wfMerge( $old, $mine, $yours, $mergedText );
 
diff --git a/tests/phpunit/includes/WikiPageTest.php b/tests/phpunit/includes/WikiPageTest.php
index fb20ce667d3..cc23d6d5e81 100644
--- a/tests/phpunit/includes/WikiPageTest.php
+++ b/tests/phpunit/includes/WikiPageTest.php
@@ -704,16 +704,7 @@ more stuff
 
 	/* @todo FIXME: fix this!
 	public function testGetUndoText() {
-		global $wgDiff3;
-
-		wfSuppressWarnings();
-		$haveDiff3 = $wgDiff3 && file_exists( $wgDiff3 );
-		wfRestoreWarnings();
-
-		if( !$haveDiff3 ) {
-			$this->markTestSkipped( "diff3 not installed or not found" );
-			return;
-		}
+		$this->checkHasDiff3();
 
 		$text = "one";
 		$page = $this->createPage( "WikiPageTest_testGetUndoText", $text );
diff --git a/tests/phpunit/includes/content/WikitextContentHandlerTest.php b/tests/phpunit/includes/content/WikitextContentHandlerTest.php
index d68c3e5438b..ed4846bed1f 100644
--- a/tests/phpunit/includes/content/WikitextContentHandlerTest.php
+++ b/tests/phpunit/includes/content/WikitextContentHandlerTest.php
@@ -103,16 +103,7 @@ class WikitextContentHandlerTest extends MediaWikiLangTestCase {
 	 * @dataProvider dataMerge3
 	 */
 	public function testMerge3( $old, $mine, $yours, $expected ) {
-		global $wgDiff3;
-
-		if ( !$wgDiff3 ) {
-			$this->markTestSkipped( "Can't test merge3(), since \$wgDiff3 is not configured" );
-		}
-
-		if ( !file_exists( $wgDiff3 ) ) {
-			#XXX: this sucks, since it uses arcane internal knowledge about TextContentHandler::merge3 and wfMerge.
-			$this->markTestSkipped( "Can't test merge3(), since \$wgDiff3 is misconfigured: can't find $wgDiff3" );
-		}
+		$this->checkHasDiff3();
 
 		// test merge
 		$oldContent = new WikitextContent( $old );