swift 在Swift中测试前置条件（或断言）

Posted 2021-05-19

import XCTest

extension XCTestCase {
    func expectingPreconditionFailure(expectedMessage: String, @noescape block: () -> ()) {

        let expectation = expectationWithDescription("failing precondition")

        // Overwrite `precondition` with something that doesn't terminate but verifies it happened.
        preconditionClosure = {
            (condition, message, file, line) in
            if !condition {
                expectation.fulfill()
                XCTAssertEqual(message, expectedMessage, "precondition message didn't match", file: file.stringValue, line: line)
            }
        }

        // Call code.
        block();

        // Verify precondition "failed".
        waitForExpectationsWithTimeout(0.0, handler: nil)

        // Reset precondition.
        preconditionClosure = defaultPreconditionClosure
    }
}

// example /////////////////////////////////////////////////////////////////////////////////////////

func doSomething() {
    precondition(false, "just not true")
}

class TestCase: XCTestCase {
    func testExpectPreconditionFailure() {
        expectingPreconditionFailure("just not true") {
            doSomething();
        }
    }
}

/// Our custom drop-in replacement `precondition`.
///
/// This will call Swift's `precondition` by default (and terminate the program).
/// But it can be changed at runtime to be tested instead of terminating.
func precondition(@autoclosure condition: () -> Bool, @autoclosure _ message: () -> String = "", file: StaticString = __FILE__, line: UWord = __LINE__) {
    preconditionClosure(condition(), message(), file, line)
}

/// The actual function called by our custom `precondition`.
var preconditionClosure: (Bool, String, StaticString, UWord) -> () = defaultPreconditionClosure
let defaultPreconditionClosure = {Swift.precondition($0, $1, file: $2, line: $3)}