XCTestCaseExtension.swift

private extension XCTestCase {
    func XCTAssertThrows<T, E>(_ expression: @autoclosure () throws -> T, specificError: E) where E: Error, E: Equatable  {

        XCTAssertThrowsError(try expression()) { error in
            XCTAssertEqual(error as? E, specificError)
        }

    }
}

//use case
class TestCase: XCTestCase {
    func testValidateWithInvalidEmailDoesThrowInvalidEmailError () {
        XCTAssertThrows(try validate(), specificError: FormError.invalidEmail)
    }
}