Add tests for checking out tags with CheckoutCommand

Change-Id: Ifec3ac59264c91e154b832fdd907736faf8a8412
Signed-off-by: Robin Stocker <robin@nibor.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CheckoutCommandTest.java

@@ -206,6 +206,28 @@ public class CheckoutCommandTest extends RepositoryTestCase {
 		assertEquals(initialCommit.name(), git.getRepository().getFullBranch());
 	}
 
+	@Test
+	public void testCheckoutLightweightTag() throws Exception {
+		git.tag().setAnnotated(false).setName("test-tag")
+				.setObjectId(initialCommit).call();
+		Ref result = git.checkout().setName("test-tag").call();
+
+		assertNull(result);
+		assertEquals(initialCommit.getId(), db.resolve(Constants.HEAD));
+		assertHeadDetached();
+	}
+
+	@Test
+	public void testCheckoutAnnotatedTag() throws Exception {
+		git.tag().setAnnotated(true).setName("test-tag")
+				.setObjectId(initialCommit).call();
+		Ref result = git.checkout().setName("test-tag").call();
+
+		assertNull(result);
+		assertEquals(initialCommit.getId(), db.resolve(Constants.HEAD));
+		assertHeadDetached();
+	}
+
 	@Test
 	public void testCheckoutRemoteTrackingWithUpstream() throws Exception {
 		Repository db2 = createRepositoryWithRemote();
@@ -326,9 +348,7 @@ public class CheckoutCommandTest extends RepositoryTestCase {
 		co = git.checkout();
 		co.setName(commitId).call();
 
-		Ref head = db.getRef(Constants.HEAD);
-		assertFalse(head.isSymbolic());
-		assertSame(head, head.getTarget());
+		assertHeadDetached();
 	}
 
 	@Test
@@ -421,6 +441,12 @@ public class CheckoutCommandTest extends RepositoryTestCase {
 		assertNull(db.resolve("HEAD"));
 	}
 
+	private void assertHeadDetached() throws IOException {
+		Ref head = db.getRef(Constants.HEAD);
+		assertFalse(head.isSymbolic());
+		assertSame(head, head.getTarget());
+	}
+
 	private void assertRepositoryCondition(int files) throws GitAPIException {
 		org.eclipse.jgit.api.Status status = this.git.status().call();
 		assertFalse(status.isClean());