Add pgm test for checkout of existing branch with checkout conflict

Add a test that checks out an existing branch with a dirty working tree
and involves a checkout conflict. This test should pass with a message:
"error: Your local changes to the following files would be overwritten
by checkout: a".

Change-Id: I5428a04a7630d9e0101404ea1aedd796f127bd7d
Signed-off-by: Axel Richard <axel.richard@obeo.fr>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.pgm.test/tst/org/eclipse/jgit/pgm/CheckoutTest.java

@@ -42,8 +42,11 @@
  */
 package org.eclipse.jgit.pgm;
 
+import java.io.File;
+
 import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.lib.CLIRepositoryTestCase;
+import org.eclipse.jgit.util.FileUtils;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -107,6 +110,29 @@ public class CheckoutTest extends CLIRepositoryTestCase {
 		assertEquals("", execute("git checkout HEAD"));
 	}
 
+	@Test
+	public void testCheckoutExistingBranchWithConflict() throws Exception {
+		Git git = new Git(db);
+		writeTrashFile("a", "Hello world a");
+		git.add().addFilepattern(".").call();
+		git.commit().setMessage("commit file a").call();
+		git.branchCreate().setName("branch_1").call();
+		git.rm().addFilepattern("a").call();
+		FileUtils.mkdirs(new File(db.getWorkTree(), "a"));
+		writeTrashFile("a/b", "Hello world b");
+		git.add().addFilepattern("a/b").call();
+		git.commit().setMessage("commit folder a").call();
+		git.rm().addFilepattern("a").call();
+		writeTrashFile("a", "New Hello world a");
+		git.add().addFilepattern(".").call();
+
+		String[] execute = execute("git checkout branch_1");
+		Assert.assertEquals(
+				"error: Your local changes to the following files would be overwritten by checkout:",
+				execute[0]);
+		Assert.assertEquals("\ta", execute[1]);
+	}
+
 	static private void assertEquals(String expected, String[] actual) {
 		// if there is more than one line, ignore last one if empty
 		Assert.assertEquals(