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NullComparisonAssertion

Issue ID NullComparisonAssertion · Severity Warning · Category Usability · Default on

Flags assertThat(x == null) (and x != null, plus the literal-on-the-left forms) where assertk's purpose-built isNull / isNotNull should be used.

Why

Comparing the value to null and asserting on the resulting Boolean works but loses information — the failure message will say "expected false, got true" instead of naming the actual value. assertk's isNotNull also transforms the assertion subject from Assert<T?> to Assert<T>, letting you chain further assertions on the non-null type without an explicit cast.

Example

import assertk.assertThat
import assertk.assertions.isFalse

fun nameExists() {
    val name: String? = this::class.simpleName
    assertThat(name == null).isFalse()
}

import assertk.assertThat
import assertk.assertions.isNotNull

fun nameExists() {
    val name: String? = this::class.simpleName
    assertThat(name).isNotNull()
}

Quick fix

Yes — the IDE collapses the binary expression and rewrites the trailing isTrue()/isFalse() into the appropriate isNull() or isNotNull(), inserting the matching import.

Pattern Becomes
assertThat(x == null).isTrue() assertThat(x).isNull()
assertThat(x == null).isFalse() assertThat(x).isNotNull()
assertThat(x != null).isTrue() assertThat(x).isNotNull()
assertThat(x != null).isFalse() assertThat(x).isNull()

Source

BooleanExpressionSubjectDetector.kt