TryCatchAssertion

Issue ID TryCatchAssertion · Severity Warning · Category Correctness · Default on

Flags simple try { ... } catch (e: Exception) { assertThat(e)... } blocks whose only purpose is to assert on an expected exception. Use assertk.assertFailure { ... } instead.

Why

A try/catch whose catch body only contains assertThat(e) calls is fragile: if you forget to put a fail() after the throwing call (or the call silently doesn't throw), the test passes when it shouldn't. assertFailure inverts the contract — the block must throw, and you assert on the captured Throwable directly.

The detector is intentionally conservative. It only fires when:

• the try block has exactly one non-fail() call, and
• the single catch clause's body contains only assertk assertThat(...) chains.

Anything else (multiple statements, mixed work, multiple catches) is left alone because the block likely exists for reasons beyond exception assertion.

Example

FlaggedPreferred

import assertk.fail
import assertk.assertThat
import assertk.assertions.isEqualTo
import assertk.assertions.prop

fun explodes() {
    val engine = RotatingDetonationEngine()
    try {
        engine.rotate()
        fail()
    } catch (e: Exception) {
        assertThat(e).prop(Exception::message).isEqualTo("Boom!")
    }
}

import assertk.assertFailure
import assertk.assertions.isEqualTo
import assertk.assertions.messageContains
import assertk.assertions.prop

fun explodes() {
    val engine = RotatingDetonationEngine()
    assertFailure { engine.rotate() }
        .prop(Throwable::message)
        .isEqualTo("Boom!")
}

Quick fix

Not provided — the rewrite is structural (delete the try/catch, extract the throwing call, hoist the catch-body assertions onto an assertFailure chain) and depends on details that can't always be inferred mechanically.

Source

TryCatchDetector.kt