Testing with Google Truth

Table of Contents

• Truth Extensions
• Test Exception
• Resource

Truth makes your test assertions and failure messages more readable. Similar to AssertJ, it natively supports many JDK and Guava types, and it is extensible to others.

• IDE auto complete, faster to type
• actual is always on the left-hand side, the expected value is always on the right-hand side.
  • So readers knows what we are testing.
• Detailed, meaningful, and easy-to-read error messages
• Hamcrest doesn’t autocomplete statements in IDEs.
• containsExactlyElementsIn
• Use containsExactly insteadof isEqualTo(ImmutableMap.of(k1,v1,k2,v2))
• containsExactly, containsAtLeast, etc are order-independent assertions; chain .inOrder() to check the order.
• Use assertWithMessage to customize error message.
• Writing your own custom subject

import static com.google.common.truth.Truth.assertThat;
import static com.google.common.truth.Truth.assertWithMessage;
// for assertions on Java 8 types
import static com.google.common.truth.Truth8.assertThat;

assertThat(theResult).isEqualTo(theExpecte);

assertThat(iterable).isEmpty();
assertThat(iterable).hasSize(x);
assertThat(iterable).containsExactly(x, y, ...);


assertThat(e).hasMessageThat().startsWith(...);
assertThat(e).hasMessageThat().contains(...);
assertThat(e).hasMessageThat().isEqualTo(...);

assertThat(map).containsExactly(key1, value1, key2, value2);
assertThat(optional).hasValue(...);
assertThat(optional).isPresent();
assertThat(optional).isEmpty();

assertThat(actualDouble).isWithin(tolerance).of(expectedDouble);

Truth Extensions

• Truth8 for java8 types such as java.util.Optional
• ProtoTruth for Message style protocol buffers and lite versions
• Re2jSubjects for use with the RE2J library

import static com.google.common.truth.Truth8.assertThat;
assertThat(javaOptional).hasValue("expectedValue");


import static com.google.common.truth.extensions.proto.ProtoTruth.assertThat;
assertThat(protoBuilder).hasAllRequiredFields();

Test Exception

• Don’t use @Rule ExpectedException
  • Any statements after the throwing call will never be executed.
• Don’t use @Test(expected = ExceptionExpectation.class)
  • The test passes if any statement throws ExceptionExpectation.
• If the method should throw FooException, test for FooException, not generic RuntimeException or its parent class.
• perform additional assertions on the exception: hasMessageThat etc if appropriate.
• Use Throwables.getCauseAs instead of (MyExpectedCause) ex.getCause()
  • Throwables.getCauseAs includes the original exception in the failure if the cause is not of the expected type

import static com.google.common.truth.Truth.assertThat;
import static org.junit.Assert.assertThrows;

IllegalArgumentException thrown =
    assertThrows(
        IllegalArgumentException.class,
        () -> list.remove(0));
assertThat(thrown).hasMessageThat().contains("Out of bounds");
assertThat(thrown).hasCauseThat().isInstanceOf(SomeOtherException.class);

assertThat(
    assertThrows(IllegalArgumentException.class,
        () -> list.remove(0)))
    .hasMessageThat().contains("Out of bounds");

Resource

• truth.dev