junit-team/junit5 · error · PreconditionViolationException

Pattern compilation failed for a regular expression…

Error message

Pattern compilation failed for a regular expression supplied in %s

What it means

Thrown by EnumSource validator validatePatterns when one of the regular expressions supplied via @CsvSource(names = ...) or @EnumSource(names = ..., mode = MATCH_ANY/MATCH_ALL) cannot be compiled by Pattern.compile. The cause is the PatternSyntaxException describing the malformed regex; the message names the @EnumSource annotation.

Solutions

Fix the regex syntax in @EnumSource(names = ...).
If you meant literal names, use the default mode (no MATCH_ANY/MATCH_ALL) so names are matched literally, or escape regex metacharacters.
Test the pattern in isolation with Pattern.compile before applying it.

Example fix

// before
@EnumSource(value = TimeUnit.class, names = "[SECONDS", mode = Mode.MATCH_ANY)

// after
@EnumSource(value = TimeUnit.class, names = ".*SECOND.*", mode = Mode.MATCH_ANY)

Defensive patterns

Strategy: validation

Validate before calling

// Compile each name pattern before running the parameterized test
for (String name : names) {
    try { Pattern.compile(name); }
    catch (PatternSyntaxException e) { throw new IllegalArgumentException("Bad regex in @EnumSource names: " + name, e); }
}

Type guard

static boolean isValidRegex(String pattern) {
    try { Pattern.compile(pattern); return true; } catch (PatternSyntaxException e) { return false; }
}

Prevention

When using MATCH_ANY/MATCH_ALL, remember @EnumSource names are regexes.
Test regex patterns in isolation first.
For literal names, omit the matching mode so names are matched exactly.

When it happens

Trigger: Supplying an invalid regular expression in @EnumSource(names = ...) with a matching mode. names.forEach(Pattern::compile) throws PatternSyntaxException for a syntactically invalid pattern.

Common situations: Unclosed character class, unbalanced parentheses, invalid quantifier, or stray regex metacharacters in the names pattern. Forgetting that names are interpreted as regexes when a MATCH mode is used.

Related errors

AI-assisted analysis of junit-team/junit5@f070c699a0 (2026-08-11). Data as JSON: /api/errors/7e2d177ce9851202. Report an issue: GitHub.

Appendix: source

Thrown at junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumSource.java:228

			Preconditions.notNull(constant, "Enum constant must not be null");
			Preconditions.notNull(names, "names must not be null");

			return selector.test(constant.name(), names);
		}

		private static void validateNames(EnumSource enumSource, Set<? extends Enum<?>> constants, Set<String> names) {
			Set<String> allNames = constants.stream().map(Enum::name).collect(toSet());
			Preconditions.condition(allNames.containsAll(names),
				() -> "Invalid enum constant name(s) in " + enumSource + ". Valid names include: " + allNames);
		}

		private static void validatePatterns(EnumSource enumSource, Set<? extends Enum<?>> constants,
				Set<String> names) {
			try {
				names.forEach(Pattern::compile);
			}
			catch (PatternSyntaxException e) {
				throw new PreconditionViolationException(
					"Pattern compilation failed for a regular expression supplied in " + enumSource, e);
			}
		}

		private interface Validator {
			void validate(EnumSource enumSource, Set<? extends Enum<?>> constants, Set<String> names);
		}

	}

}

View on GitHub (pinned to f070c699a0)