ChangeIT: Fix/improve tests for CreateMergePatchSet REST endpoint

1. Instead of creating and pushing a commit to have a start commit,
   just retrieve the already existing commit from the master branch.
2. Rename the variable for the start commit from 'start' to
   'initialHead' to have the naming consistent with the other tests.
3. Create the dev branch before pushing a commit to the master branch,
   so that the commit that is pushed to the dev branch is a sibling and
   not a follow-up commit. This way we test a real merge and not just
   the fast-forward merge case. This requires to reset the testRepo to
   the start commit before creating and pushing a commit to the dev
   branch.
4. Remove the redundant call to PushOneCommit.Result#assertOkStatus()
   after calling createChange(). The createChange() method already calls
   assertOkStatus().

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I672c5e784a006cb65b8d193daea6f821e1cbfb38

javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java

@@ -3167,20 +3167,19 @@ public class ChangeIT extends AbstractDaemonTest {
 
   @Test
   public void createMergePatchSet() throws Exception {
-    PushOneCommit.Result start = pushTo("refs/heads/master");
+    RevCommit initialHead = projectOperations.project(project).getHead("master");
-    start.assertOkStatus();
+    createBranch("dev");
-    // create a change for master
-    PushOneCommit.Result r = createChange();
-    r.assertOkStatus();
-    String changeId = r.getChangeId();
 
-    testRepo.reset(start.getCommit());
+    // create a change for master
+    String changeId = createChange().getChangeId();
+
+    testRepo.reset(initialHead);
     PushOneCommit.Result currentMaster = pushTo("refs/heads/master");
     currentMaster.assertOkStatus();
     String parent = currentMaster.getCommit().getName();
 
     // push a commit into dev branch
-    createBranch("dev");
+    testRepo.reset(initialHead);
     PushOneCommit.Result changeA =
         pushFactory
             .create(user.newIdent(), testRepo, "change A", "A.txt", "A content")
@@ -3202,21 +3201,21 @@ public class ChangeIT extends AbstractDaemonTest {
 
   @Test
   public void createMergePatchSetInheritParent() throws Exception {
-    PushOneCommit.Result start = pushTo("refs/heads/master");
+    RevCommit initialHead = projectOperations.project(project).getHead("master");
-    start.assertOkStatus();
+    createBranch("dev");
+
     // create a change for master
     PushOneCommit.Result r = createChange();
-    r.assertOkStatus();
     String changeId = r.getChangeId();
     String parent = r.getCommit().getParent(0).getName();
 
     // advance master branch
-    testRepo.reset(start.getCommit());
+    testRepo.reset(initialHead);
     PushOneCommit.Result currentMaster = pushTo("refs/heads/master");
     currentMaster.assertOkStatus();
 
     // push a commit into dev branch
-    createBranch("dev");
+    testRepo.reset(initialHead);
     PushOneCommit.Result changeA =
         pushFactory
             .create(user.newIdent(), testRepo, "change A", "A.txt", "A content")