AssertJ Tutorials

Learn how to set up and use AssertJ fluent assertions in Java projects with Maven or Gradle.

Explore AssertJ's rich set of string assertions including contains, startsWith, matches, and more.

Learn how to use AssertJ to assert on Lists, Sets, and other Collections with contains, hasSize, filteredOn, and extracting.

Learn how to use AssertJ's extracting and filteredOn methods to assert on properties of collection elements.

Learn how to assert on exceptions thrown by code using AssertJ's assertThatThrownBy and catchThrowable.

Learn how to assert on Java Map entries, keys, and values using AssertJ.

Use AssertJ to assert on integers, doubles, and BigDecimals including range and offset comparisons.

Learn how to assert on Java Optional values using AssertJ's isPresent, isEmpty, hasValue, and more.

Learn how to use AssertJ's as() method to add descriptive context to assertion failure messages.

Learn how to override AssertJ's default error messages using withFailMessage and overridingErrorMessage.

Learn how to use AssertJ SoftAssertions to collect multiple assertion failures instead of stopping at the first one.

Use AssertJ's BDDAssertions to write Given-When-Then style tests with then() instead of assertThat().

Learn how to create domain-specific custom assertion classes in AssertJ by extending AbstractAssert.

Learn how to create reusable AssertJ Condition objects and combine them with allOf, anyOf, and not.

Use AssertJ's usingRecursiveComparison to deeply compare object graphs without overriding equals().

Assert on Java 8 date and time types like LocalDate, LocalDateTime, and Instant using AssertJ.

Use AssertJ to assert on File and Path objects including existence, content, and directory checks.

Learn about common incorrect usages of AssertJ assertions and how to avoid them.