Assertion description

It is often valuable to describe the assertion performed, especially for boolean assertions where the default error message just complains that it got false instead of true (or vice versa).

You can set such a description with as(String description, Object… args) but remember to do it before calling the assertion otherwise it is simply ignored as a failing assertion breaks the chained calls.

Example of a failing assertion with a description:

TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, Race.HOBBIT);

// failing assertion, remember to call as() before the assertion!
assertThat(frodo.getAge()).as("check %s's age", frodo.getName())
                          .isEqualTo(100);

The error message starts with the given description in [] :

[check Frodo's age] expected:<100> but was:<33>

Printing or consuming description

AssertJ can print each assertion description (when it is set), to do so call Assertions.setPrintAssertionsDescription(true);.

If printing assertion descriptions is not what you need, you can alternatively register a Consumer<Description> that will be called each time a description is set.

Both options are exposed in AssertJ Configuration class.

Example: using a description consumer

// initialize the description consumer
final StringBuilder descriptionReportBuilder = new StringBuilder(String.format("Assertions:%n"));
Consumer<Description> descriptionConsumer = desc -> descriptionReportBuilder.append(String.format("-- %s%n", desc));

// use the description consumer for any following assertions descriptions.
Assertions.setDescriptionConsumer(descriptionConsumer);

// execute some assertions
TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, Race.HOBBIT);
assertThat(frodo.getName()).as("check name")
                          .isEqualTo("Frodo");
assertThat(frodo.getAge()).as("check age")
                          .isEqualTo(33);

// get the report
String descriptionReport = descriptionReportBuilder.toString();

resulting descriptionReport:

Assertions:
-- check name
-- check age