fluent-assert

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

• Read references/FULL-API.md when you need supported type coverage, installation snippets, or a fuller example.
• Use evals/evals.json as the regression prompt set when changing this skill.