Add static methods for constructing null aware Correspondences

This avoids some code duplication for implementing Correspondences that
want to map null values to null.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I614d32d7b9a29e2332fbc220b37fd5325bc84b56

java/com/google/gerrit/truth/NullAwareCorrespondence.java

@@ -0,0 +1,92 @@
+// Copyright (C) 2020 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
+// Copyright (C) 2020 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.truth;
+
+import com.google.common.base.Function;
+import com.google.common.truth.Correspondence;
+import java.util.Optional;
+
+/** Utility class for constructing null aware {@link Correspondence}s. */
+public class NullAwareCorrespondence {
+  /**
+   * Constructs a {@link Correspondence} that compares elements by transforming the actual elements
+   * using the given function and testing for equality with the expected elements.
+   *
+   * <p>If the actual element is null, it will correspond to a null expected element. This is
+   * different to {@link Correspondence#transforming(Function, String)} which would invoke the
+   * function with a {@code null} argument, requiring the function being able to handle {@code
+   * null}.
+   *
+   * @param actualTransform a {@link Function} taking an actual value and returning a new value
+   *     which will be compared with an expected value to determine whether they correspond
+   * @param description should fill the gap in a failure message of the form {@code "not true that
+   *     <some actual element> is an element that <description> <some expected element>"}, e.g.
+   *     {@code "has an ID of"}
+   */
+  public static <A, E> Correspondence<A, E> transforming(
+      Function<A, ? extends E> actualTransform, String description) {
+    return Correspondence.transforming(
+        actualValue -> Optional.ofNullable(actualValue).map(actualTransform).orElse(null),
+        description);
+  }
+
+  /**
+   * Constructs a {@link Correspondence} that compares elements by transforming the actual elements
+   * using the given function and testing for equality with the expected elements.
+   *
+   * <p>If the actual element is null, it will correspond to a null expected element. This is
+   * different to {@link Correspondence#transforming(Function, Function, String)} which would invoke
+   * the function with a {@code null} argument, requiring the function being able to handle {@code
+   * null}.
+   *
+   * <p>If the expected element is null, it will correspond to a new null expected element. This is
+   * different to {@link Correspondence#transforming(Function, Function, String)} which would invoke
+   * the function with a {@code null} argument, requiring the function being able to handle {@code
+   * null}.
+   *
+   * @param actualTransform a {@link Function} taking an actual value and returning a new value
+   *     which will be compared with an expected value to determine whether they correspond
+   * @param expectedTransform a {@link Function} taking an expected value and returning a new value
+   *     which will be compared with a transformed actual value
+   * @param description should fill the gap in a failure message of the form {@code "not true that
+   *     <some actual element> is an element that <description> <some expected element>"}, e.g.
+   *     {@code "has an ID of"}
+   */
+  public static <A, E> Correspondence<A, E> transforming(
+      Function<A, ? extends E> actualTransform,
+      Function<E, ?> expectedTransform,
+      String description) {
+    return Correspondence.transforming(
+        actualValue -> Optional.ofNullable(actualValue).map(actualTransform).orElse(null),
+        expectedValue -> Optional.ofNullable(expectedValue).map(expectedTransform).orElse(null),
+        description);
+  }
+
+  /**
+   * Private constructor to prevent instantiation of this class.
+   *
+   * <p>This class contains only static method and hence never needs to be instantiated.
+   */
+  private NullAwareCorrespondence() {}
+}

javatests/com/google/gerrit/acceptance/api/accounts/AccountIT.java

@@ -148,6 +148,7 @@ import com.google.gerrit.server.validators.AccountActivationValidationListener;
 import com.google.gerrit.server.validators.ValidationException;
 import com.google.gerrit.testing.ConfigSuite;
 import com.google.gerrit.testing.FakeEmailSender.Message;
+import com.google.gerrit.truth.NullAwareCorrespondence;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import com.jcraft.jsch.KeyPair;
@@ -161,7 +162,6 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -2901,12 +2901,7 @@ public class AccountIT extends AbstractDaemonTest {
   }
 
   private static Correspondence<GroupInfo, String> getGroupToNameCorrespondence() {
-    return Correspondence.from(
-        (actualGroup, expectedName) -> {
-          String groupName = actualGroup == null ? null : actualGroup.name;
-          return Objects.equals(groupName, expectedName);
-        },
-        "has name");
+    return NullAwareCorrespondence.transforming(groupInfo -> groupInfo.name, "has name");
   }
 
   private void assertSequenceNumbers(List<SshKeyInfo> sshKeys) {

javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java

@@ -100,6 +100,7 @@ import com.google.gerrit.server.notedb.Sequences;
 import com.google.gerrit.server.util.MagicBranch;
 import com.google.gerrit.server.util.time.TimeUtil;
 import com.google.gerrit.testing.GerritJUnit.ThrowingRunnable;
+import com.google.gerrit.truth.NullAwareCorrespondence;
 import com.google.inject.AbstractModule;
 import com.google.inject.Inject;
 import com.google.inject.Module;
@@ -111,7 +112,6 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
 import java.util.stream.Stream;
 import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
 import org.eclipse.jgit.junit.TestRepository;
@@ -1517,12 +1517,8 @@ public class GroupsIT extends AbstractDaemonTest {
   }
 
   private static Correspondence<AccountInfo, String> getAccountToUsernameCorrespondence() {
-    return Correspondence.from(
-        (actualAccount, expectedName) -> {
-          String username = actualAccount == null ? null : actualAccount.username;
-          return Objects.equals(username, expectedName);
-        },
-        "has username");
+    return NullAwareCorrespondence.transforming(
+        accountInfo -> accountInfo.username, "has username");
   }
 
   private void assertStaleGroupAndReindex(AccountGroup.UUID groupUuid) throws IOException {

javatests/com/google/gerrit/acceptance/testsuite/group/GroupOperationsImplTest.java

@@ -29,9 +29,9 @@ import com.google.gerrit.extensions.api.groups.GroupInput;
 import com.google.gerrit.extensions.common.AccountInfo;
 import com.google.gerrit.extensions.common.GroupInfo;
 import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.truth.NullAwareCorrespondence;
 import com.google.inject.Inject;
 import java.sql.Timestamp;
-import java.util.Objects;
 import java.util.Optional;
 import org.junit.Test;
 
@@ -616,28 +616,11 @@ public class GroupOperationsImplTest extends AbstractDaemonTest {
   }
 
   private static Correspondence<AccountInfo, Account.Id> getAccountToIdCorrespondence() {
-    return Correspondence.from(
-        (actualAccount, expectedId) -> {
-          Account.Id accountId =
-              Optional.ofNullable(actualAccount)
-                  .map(account -> account._accountId)
-                  .map(Account::id)
-                  .orElse(null);
-          return Objects.equals(accountId, expectedId);
-        },
-        "has ID");
+    return NullAwareCorrespondence.transforming(
+        account -> Account.id(account._accountId), "has ID");
   }
 
   private static Correspondence<GroupInfo, AccountGroup.UUID> getGroupToUuidCorrespondence() {
-    return Correspondence.from(
-        (actualGroup, expectedUuid) -> {
-          AccountGroup.UUID groupUuid =
-              Optional.ofNullable(actualGroup)
-                  .map(group -> group.id)
-                  .map(AccountGroup::uuid)
-                  .orElse(null);
-          return Objects.equals(groupUuid, expectedUuid);
-        },
-        "has UUID");
+    return NullAwareCorrespondence.transforming(group -> AccountGroup.uuid(group.id), "has UUID");
   }
 }