| name | fluent-assert |
| description | Use when writing or refactoring Kotlin tests that need assertions, including JUnit tests, Wow/SagaSpec tests, JDK types, nullable values, collections, maps, time values, futures, predicates, custom data classes, or exception assertions with assertThrownBy. |
FluentAssert
Use FluentAssert for Kotlin assertions in this repository and in downstream Kotlin test examples. Prefer the Kotlin extension style over direct AssertJ calls.
Core Rule
import me.ahoo.test.asserts.assert
actual.assert().isEqualTo(expected)
Avoid assertThat(actual) in ordinary test code. FluentAssert keeps nullable receivers natural:
val name: String? = null
name.assert().isNull()
Common Patterns
| Need | Pattern |
|---|
| Primitive/string/object | value.assert().isEqualTo(expected) |
| Collection/list/map | items.assert().hasSize(2).contains("a") |
| Nullable value | value.assert().isNull() or value.assert().isNotNull() |
| Exception lambda | assertThrownBy<IllegalArgumentException> { call() }.hasMessage("bad") |
| Existing exception | throwable.assert().hasMessageContaining("bad") |
| Time month checks | date.assert().hasMonth(Month.APRIL) |
| Future success/failure | future.assert().isCompletedWithValue(value) / .isCompletedExceptionally() |
| Recursive comparison | actual.assert().usingRecursiveComparison().isEqualTo(expected) |
For exception lambdas, also import:
import me.ahoo.test.asserts.assertThrownBy
For month assertions, import java.time.Month; AssertJ expects Month, not an integer.
Wow/Saga Tests
Use FluentAssert inside expectation blocks too:
expectCommandBody<UpdateDemo> {
data.assert().isNotNull().isEqualTo("updated")
}
AssertProvider
For types implementing AssertJ's AssertProvider<A>, .assert() returns the provider's custom assertion type:
provider.assert().isPositive()
Only use direct assertThat when implementing the provider's assertThat() method or when a project explicitly requires raw AssertJ.
Avoid
- Do not chain
.assert() after assertThrownBy; it already returns ThrowableAssert<T>.
- Do not assert contradictory states on one value, such as
Optional.of("x").assert().isPresent().isEmpty().
- Do not use unavailable AssertJ shortcuts like
OffsetDateTimeAssert.hasOffset(...).
- Do not use numeric
hasMonth(4) for LocalDate or YearMonth; use hasMonth(Month.APRIL).
- Do not switch to
assertThat(value).usingRecursiveComparison(); keep chaining from value.assert().
References
