Add one more test to ReadTreeTest

Add an explicit test case to check that we don't
overwrite dirty files in case Head & Index are
equal.

Change-Id: I6266d0a449e55369d2d0a048694dca5565c5fcf3
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ReadTreeTest.java

@@ -657,6 +657,20 @@ public abstract class ReadTreeTest extends RepositoryTestCase {
 		assertTrue(new File(trash, "foo").isFile());
 	}
 
+	public void testDontOverwriteDirtyFile() throws IOException {
+		setupCase(mk("foo"), mk("other"), mk("foo"));
+		writeTrashFile("foo", "different");
+		try {
+			checkout();
+			fail("Didn't got the expected conflict");
+		} catch (CheckoutConflictException e) {
+			assertIndex(mk("foo"));
+			assertWorkDir(mkmap("foo", "different"));
+			assertTrue(getConflicts().equals(Arrays.asList("foo")));
+			assertTrue(new File(trash, "foo").isFile());
+		}
+	}
+
 	/**
 	 * The interface these tests need from a class implementing a checkout
 	 */