XCTAssert: The Pass/Fail Gatekeeper of Your Tests

XCTAssert functions are the assertions that make a test a test, acting as gatekeepers that check if your code's output matches expectations. Inside any test method, you'll use functions like `XCTAssertEqual` or `XCTAssertNil` to validate outcomes. The biggest footgun is writing a test that just runs code. A test without an `XCTAssert` will always pass unless it crashes, giving you a false sense of security about your code's correctness and creating a "green" but useless test suite.