RefUpdateUtil: Add a method to delete a ref unconditionally

Did you know that deleting a single ref using RefUpdate returns the
result NEW when the ref didn't exist? Me neither. That's exactly why we
have this class, rather than requiring programmers to remember absurd
JGit semantics.

Change-Id: I8e963da1a74f6e25394c14be8e171176804702b6

javatests/com/google/gerrit/server/update/RefUpdateUtilRepoTest.java

@@ -0,0 +1,117 @@
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.update;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.io.MoreFiles;
+import com.google.common.io.RecursiveDeleteOption;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import org.eclipse.jgit.internal.storage.dfs.DfsRepositoryDescription;
+import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
+import org.eclipse.jgit.internal.storage.file.FileRepository;
+import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.lib.Repository;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameter;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class RefUpdateUtilRepoTest {
+  public enum RepoSetup {
+    LOCAL_DISK {
+      @Override
+      Repository setUpRepo() throws Exception {
+        Path p = Files.createTempDirectory("gerrit_repo_");
+        try {
+          Repository repo = new FileRepository(p.toFile());
+          repo.create(true);
+          return repo;
+        } catch (Exception e) {
+          delete(p);
+          throw e;
+        }
+      }
+
+      @Override
+      void tearDownRepo(Repository repo) throws Exception {
+        delete(repo.getDirectory().toPath());
+      }
+
+      private void delete(Path p) throws Exception {
+        MoreFiles.deleteRecursively(p, RecursiveDeleteOption.ALLOW_INSECURE);
+      }
+    },
+
+    IN_MEMORY {
+      @Override
+      Repository setUpRepo() {
+        return new InMemoryRepository(new DfsRepositoryDescription("repo"));
+      }
+
+      @Override
+      void tearDownRepo(Repository repo) {}
+    };
+
+    abstract Repository setUpRepo() throws Exception;
+
+    abstract void tearDownRepo(Repository repo) throws Exception;
+  }
+
+  @Parameters(name = "{0}")
+  public static ImmutableList<RepoSetup[]> data() {
+    return ImmutableList.copyOf(new RepoSetup[][] {{RepoSetup.LOCAL_DISK}, {RepoSetup.IN_MEMORY}});
+  }
+
+  @Parameter public RepoSetup repoSetup;
+
+  private Repository repo;
+
+  @Before
+  public void setUp() throws Exception {
+    repo = repoSetup.setUpRepo();
+  }
+
+  @After
+  public void tearDown() throws Exception {
+    if (repo != null) {
+      repoSetup.tearDownRepo(repo);
+      repo = null;
+    }
+  }
+
+  @Test
+  public void deleteRefNoOp() throws Exception {
+    String ref = "refs/heads/foo";
+    assertThat(repo.exactRef(ref)).isNull();
+    RefUpdateUtil.deleteChecked(repo, "refs/heads/foo");
+    assertThat(repo.exactRef(ref)).isNull();
+  }
+
+  @Test
+  public void deleteRef() throws Exception {
+    String ref = "refs/heads/foo";
+    new TestRepository<>(repo).branch(ref).commit().create();
+    assertThat(repo.exactRef(ref)).isNotNull();
+    RefUpdateUtil.deleteChecked(repo, "refs/heads/foo");
+    assertThat(repo.exactRef(ref)).isNull();
+  }
+}