public Class SoftAssertions

Suppose we have a test case and in it we'd like to make numerous assertions. In this case, we're hosting a dinner party and we want to ensure not only that all our guests survive but also that nothing in the mansion has been unduly disturbed:

 @Test
public void host_dinner_party_where_nobody_dies() {
  Mansion mansion = new Mansion();
  mansion.hostPotentiallyMurderousDinnerParty();
  assertThat(mansion.guests()).as("Living Guests").isEqualTo(7);
  assertThat(mansion.kitchen()).as("Kitchen").isEqualTo("clean");
  assertThat(mansion.library()).as("Library").isEqualTo("clean");
  assertThat(mansion.revolverAmmo()).as("Revolver Ammo").isEqualTo(6);
  assertThat(mansion.candlestick()).as("Candlestick").isEqualTo("pristine");
  assertThat(mansion.colonel()).as("Colonel").isEqualTo("well kempt");
  assertThat(mansion.professor()).as("Professor").isEqualTo("well kempt");
}

After running the test, JUnit provides us with the following exception message:

 org.junit.ComparisonFailure: [Living Guests] expected:<[7]> but was:<[6]>

Oh no! A guest has been murdered! But where, how, and by whom?

Unfortunately frameworks like JUnit halt the test upon the first failed assertion. Therefore, to collect more evidence, we'll have to rerun the test (perhaps after attaching a debugger or modifying the test to skip past the first assertion). Given that hosting dinner parties takes a long time, this seems rather inefficient.

Instead let's change the test so that at its completion we get the result of all assertions at once. We can do that by using a SoftAssertions instance instead of the static methods on Assertions as follows:

 @Test
public void host_dinner_party_where_nobody_dies() {
  Mansion mansion = new Mansion();
  mansion.hostPotentiallyMurderousDinnerParty();
  SoftAssertions softly = new SoftAssertions();
  softly.assertThat(mansion.guests()).as("Living Guests").isEqualTo(7);
  softly.assertThat(mansion.kitchen()).as("Kitchen").isEqualTo("clean");
  softly.assertThat(mansion.library()).as("Library").isEqualTo("clean");
  softly.assertThat(mansion.revolverAmmo()).as("Revolver Ammo").isEqualTo(6);
  softly.assertThat(mansion.candlestick()).as("Candlestick").isEqualTo("pristine");
  softly.assertThat(mansion.colonel()).as("Colonel").isEqualTo("well kempt");
  softly.assertThat(mansion.professor()).as("Professor").isEqualTo("well kempt");
  softly.assertAll();
}

Now upon running the test our JUnit exception message is far more detailed:

 org.assertj.core.api.SoftAssertionError: The following 4 assertions failed:
1) [Living Guests] expected:<[7]> but was:<[6]>
2) [Library] expected:<'[clean]'> but was:<'[messy]'>
3) [Candlestick] expected:<'[pristine]'> but was:<'[bent]'>
4) [Professor] expected:<'[well kempt]'> but was:<'[bloodied and disheveled]'>

Aha! It appears that perhaps the Professor used the candlestick to perform the nefarious deed in the library. We should let the police take it from here.

You can also use the static method assertSoftly. the assertAll method will be called automatically after the lambda function completes.

 @Test
public void host_dinner_party_where_nobody_dies() {
  Mansion mansion = new Mansion();
  mansion.hostPotentiallyMurderousDinnerParty();
  SoftAssertions.assertSoftly(softly -> {
    softly.assertThat(mansion.guests()).as("Living Guests").isEqualTo(7);
    softly.assertThat(mansion.kitchen()).as("Kitchen").isEqualTo("clean");
    softly.assertThat(mansion.library()).as("Library").isEqualTo("clean");
    softly.assertThat(mansion.revolverAmmo()).as("Revolver Ammo").isEqualTo(6);
    softly.assertThat(mansion.candlestick()).as("Candlestick").isEqualTo("pristine");
    softly.assertThat(mansion.colonel()).as("Colonel").isEqualTo("well kempt");
    softly.assertThat(mansion.professor()).as("Professor").isEqualTo("well kempt");
  });
}

You can also compose several soft assertions together using the SoftAssertionsProvider#assertAlso(AssertionErrorCollector) method

 public SoftAssertions check_kitchen() {
  SoftAssertions softly = new SoftAssertions();
  softly.assertThat(mansion.kitchen()).as("Kitchen").isEqualTo("clean");
  return softly;
}

public SoftAssertions check_library() {
  SoftAssertions softly = new SoftAssertions();
  softly.assertThat(mansion.library()).as("Library").isEqualTo("clean");
  return softly;
}

@Test
public void host_dinner_party_where_nobody_dies() {
  Mansion mansion = new Mansion();
  mansion.hostPotentiallyMurderousDinnerParty();
  softly.assertThat(mansion.guests()).as("Living Guests").isEqualTo(7);
  softly.assertThat(mansion.revolverAmmo()).as("Revolver Ammo").isEqualTo(6);
  softly.assertThat(mansion.candlestick()).as("Candlestick").isEqualTo("pristine");
  softly.assertThat(mansion.colonel()).as("Colonel").isEqualTo("well kempt");
  softly.assertThat(mansion.professor()).as("Professor").isEqualTo("well kempt");

  SoftAssertions kitchen = check_kitchen();
  softly.assertAlso(kitchen);

  SoftAssertions library = check_library();
  softly.assertAlso(library);

  softly.assertAll();
}

SoftAssertions works by providing you with proxies of the AssertJ assertion objects (those created by Assertions#assertThat...) whose assertion failures are caught and stored. Only when you call SoftAssertionsProvider#assertAll() will a SoftAssertionError be thrown containing the error messages of those previously caught assertion failures.

Note that because SoftAssertions is stateful you should use a new instance of SoftAssertions per test method. Also, if you forget to call assertAll() at the end of your test, the test will pass even if any assertion objects threw exceptions (because they're proxied, remember?). So don't forget. You might use JUnitSoftAssertions or AutoCloseableSoftAssertions to get assertAll() to be called automatically.

It is recommended to use AbstractAssert#as(String, Object...) so that the multiple failed assertions can be easily distinguished from one another.