AssertJ assertions allMatch and doesNotContain on an empty list always returns true whatever the content of the
predicate. Despite being correct, you should make explicit if you expect an empty list or not, by adding
isEmpty()/isNotEmpty() in addition to calling the assertion, or by testing the list’s content further. It will justify the
useless predicate to improve clarity or increase the reliability of the test.
This rule raises an issue when any of the methods listed are used without asserting that the list is empty or not and without testing the
content.
Targetted methods:
-
allMatch
-
allSatisfy
-
doesNotContain
-
doesNotContainSequence
-
doesNotContainSubsequence
-
doesNotContainAnyElementsOf
Noncompliant code example
List<String> logs = getLogs();
assertThat(logs).allMatch(e -> e.contains(“error”)); // Noncompliant, this test pass if logs are empty!
assertThat(logs).doesNotContain("error"); // Noncompliant, do you expect any log?
Compliant solution
List<String> logs = getLogs();
assertThat(logs).isNotEmpty().allMatch(e -> e.contains(“error”));
// Or
assertThat(logs).hasSize(5).allMatch(e -> e.contains(“error”));
// Or
assertThat(logs).isEmpty();
// Despite being redundant, this is also acceptable since it explains why you expect an empty list
assertThat(logs).doesNotContain("error").isEmpty();
// or test the content of the list further
assertThat(logs).contains("warning").doesNotContain("error");
