fix assert<T>(T?, T -> Bool)

[ishkawa]

Fix assert("foo", { $0.isEmpty }) passes tests.

[robrix]

Why is this change necessary? The tests on master pass as-is.

[ishkawa]

Because assert<T>(T?, T -> Bool) does not work as expected. It does not fail even if the closure returned false. For example, assert("foo", { $0.isEmpty }) (string is not empty) and assert(string, { s in false }).

I tried to add test that expresses assert<T>(T?, T -> Bool) fails as expected, but I could not write test that passes if XCTFail is called as expected.

[robrix]

Ah, good catch—thank you! 🙇

[ishkawa]

👌

[robrix]

I think the only way we could reasonably test assertion failure would be to fork off xcodebuild runs. That seems a bit heavyweight for now, but it would be nice to have the assertions verified automatically.

[robrix]

(Alternatively, we might be able to construct a custom XCTest at runtime and test against its values. But I’m unsure whether that would actually work; it would depend on how XCTFail bubbles its failure state upwards.)

[ishkawa]

I found overriding XCTestCase.recordFailureWithDescription() gives us chance to determine if a failure is expected or not. As a result, following test code finishes with success.

final class AssertionsTests: XCTestCase {
    var expectingFailure = false
    var expectedFailureOccurred = false

    override func recordFailureWithDescription(description: String!, inFile filePath: String!, atLine lineNumber: UInt, expected: Bool) {
        if expectingFailure {
            expectedFailureOccurred = true
        } else {
            super.recordFailureWithDescription(description, inFile: filePath, atLine: lineNumber, expected: false)
        }
    }

    func expectFailure(test: Void -> Void) {
        expectingFailure = true
        expectedFailureOccurred = false
        test()
        expectingFailure = false
        XCTAssert(expectedFailureOccurred)
    }

    func testAssertFailure() {
        expectFailure {
            assert(" ", { $0.isEmpty }) // calls XCTFail but is not collected as a failure
        }
    }

    func testAssertSuccess() {
        assert("", { $0.isEmpty })
    }
}

I'm not sure that this kind of code should be used in tests of this library.

[robrix]

Cool, thank you for sharing that! That’s much simpler than I expected we could manage, and I think it’d be a great addition to the tests 👍