Support nullable Java Date/Time arguments in @ParameterizedTest methods

[Clemens-L]

When supplying a Java Time parameter in parameterized tests, it is not possible to null the parameter by supplying a null-String:

junit5/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverter.java

Lines 52 to 56 in 6be5547

	@Override
	protected Object convert(Object input, Class<?> targetClass, JavaTimeConversionPattern annotation) {
	if (input == null) {
	throw new ArgumentConversionException("Cannot convert null to " + targetClass.getName());
	}

In my tests, it would come in handy if I could just set a null string in my CsvSource and have the JavaTimeArgumentConverter null the Java Time parameter.

I would suggest making this behaviour configurable via the JavaTimeConversionPattern annotation, such as:

@ParameterizedTest
@CsvSource({", 01.01.1970", "01.01.1970, 01.01.1970"})
void test(
    @JavaTimeConversionPattern("dd.MM.yyyy", nullable = true) LocalDate nullableDate,
    @JavaTimeConversionPattern("dd.MM.yyyy") LocalDate nonNullableDate) {
    // ...
}

(with the old behaviour being the default).

Let me know what you think. If you deem this feature useful, I'd be happy to provide a PR for this.

Deliverables

• Option to have JavaTimeArgumentConverter convert null-values

[marcphilipp]

Thanks for raising this! I think your proposed solution makes sense. We should point to the new nullable attribute in the message of the ArgumentConversionException when it's set to false.

[Clemens-L]

Hi @marcphilipp,

good to hear! I opened a PR and included your suggestion to mention the nullable option in the ArgumentConversionException. Let me know if I should change anything.

Thanks!

[sbrannen]

@Clemens-L, congratulations on submitting your first issue and your first PR for JUnit 5! 👍

Your PR has been merged into main in e8c92f8.

Thanks