System property extension

While looking for a way to handle system properties in JUnit 5 tests on Stack Overflow, I came up with the following extension (see this gist) based on the provided answer:

class SystemPropertyExtensionTest {

	@BeforeAll
	static void setUpOnce() {
		System.setProperty( "some property", "old value" );
	}

	@SystemProperty( key = "some property" )
	@Test
	void extension_should_set_property_to_null() {
		Assertions.assertNull( System.getProperty( "some property" ) );
	}

	@SystemProperty( key = "some property", value = "new value" )
	@Test
	void extension_should_set_property_to_value() {
		Assertions.assertEquals( System.getProperty( "some property" ), "new value" );
	}

	@SystemProperty( key = "some property" )
	@SystemProperty( key = "another property", value = "new value" )
	@Test
	void extension_should_be_repeatable() {
		Assertions.assertNull( System.getProperty( "some property" ) );
		Assertions.assertEquals( System.getProperty( "another property" ), "new value" );
	}

	@AfterAll
	static void tearDownOnce() {
		Assertions.assertEquals( System.getProperty( "some property" ), "old value" );
	}

}

After posting it on Twitter, @sbrannen drew my attention to JUnit Pioneer. I would be happy to submit a PR, which is why I have opened this question to debate the solution.

IMHO there are currently two minor issues:

• The annotation probably should be repeatable (as already pointed out on Stack Overflow), in case somebody has to use more than one property. (Adapted gist accordingly.)
• Since null is not allowed for default values, I have picked "" to see if the property only needs to be cleared or set to a specific value. Are there situations where someone has to set a property to an empty string, where this wouldn’t work anymore?

[sormuras]

Back-linked the associated PR #133 and…

So, in the interim, it might make sense to go ahead and get the proposed @SystemProperty support in JUnit Pioneer.

…I second this. Let’s get it in, @nicolaiparlog 🚀

[nipafx]

I like @ClearSystemProperty - very clear, no ambiguity.