TruthSelfEquals
isEqualTo should not be used to test an object for equality with itself; the assertion will never fail.

Category
TRUTH
Severity
ERROR
Maturity

The problem

If a test subject and the argument to isEqualTo are the same instance (e.g. assertThat(x).isEqualTo(x)), then the assertion will always pass. Truth implements isEqualTo using [Objects#equal] , which tests its arguments for reference equality and returns true without calling equals() if both arguments are the same instance.

To test the implementation of an equals method, use Guava’s EqualsTester.

Suppression

Suppress false positives by adding an @SuppressWarnings("TruthSelfEquals") annotation to the enclosing element.


Positive examples

TruthSelfEqualsPositiveCases.java

/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * 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.errorprone.bugpatterns.testdata;

import static com.google.common.truth.Truth.assertThat;
import static com.google.common.truth.Truth.assertWithMessage;

/**
 * Positive test cases for TruthSelfEquals check.
 *
 * @author bhagwani@google.com (Sumit Bhagwani)
 */
public class TruthSelfEqualsPositiveCases {

  public void testAssertThatEq() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: new EqualsTester().addEqualityGroup(test).testEquals()
    assertThat(test).isEqualTo(test);
  }

  public void testAssertWithMessageEq() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: new EqualsTester().addEqualityGroup(test).testEquals()
    assertWithMessage("msg").that(test).isEqualTo(test);
  }

  public void testAssertThatSame() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: new EqualsTester().addEqualityGroup(test).testEquals()
    assertThat(test).isSameAs(test);
  }

  public void testAssertWithMessageSame() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: new EqualsTester().addEqualityGroup(test).testEquals()
    assertWithMessage("msg").that(test).isSameAs(test);
  }

  public void testAssertThatNeq() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: isNotEqualTo method are the same object
    assertThat(test).isNotEqualTo(test);
  }

  public void testAssertThatNotSame() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: isNotSameAs method are the same object
    assertThat(test).isNotSameAs(test);
  }

  public void testAssertWithMessageNeq() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: isNotEqualTo method are the same object
    assertWithMessage("msg").that(test).isNotEqualTo(test);
  }

  public void testAssertWithMessageNotSame() {
    String test = Boolean.TRUE.toString();
    // BUG: Diagnostic contains: isNotSameAs method are the same object
    assertWithMessage("msg").that(test).isNotSameAs(test);
  }
}

Negative examples

TruthSelfEqualsNegativeCases.java

/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * 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.errorprone.bugpatterns.testdata;

import static com.google.common.truth.Truth.assertThat;

/**
 * Negative test cases for TruthSelfEquals check.
 *
 * @author bhagwani@google.com (Sumit Bhagwani)
 */
public class TruthSelfEqualsNegativeCases {

  public void testEq() {
    assertThat(Boolean.TRUE.toString()).isEqualTo(Boolean.FALSE.toString());
  }

  public void testNeq() {
    assertThat(Boolean.TRUE.toString()).isNotEqualTo(Boolean.FALSE.toString());
  }
}