Swift Unit testing with XCTAssertThrows analogue - swift

Question

Is there any equivalent to check for throwing exceptions in swift language Unit tests?
For example I Have a class:
class Square : NSObject{
let sideLength: Int
init(sideLength: Int) {
assert(sideLength >= 0, "Wrong initialization of Square class with below zero side length")
self.sideLength = sideLength
super.init()
}
}
and Test to check it work. In objective C I can write test method like this:
- (void)testInitializationWithWrongSideLengthThrowsExceptions{
XCTAssertThrows([[Shape alloc] initWithSideLength: -50], "Should throw exceptions on wrong side values initialisations");
}
What is Swift equal technic?

Answer 1

If you add the following three files to your tests:
// ThrowsToBool.h
#import <Foundation/Foundation.h>
/// A 'pure' closure; has no arguments, returns nothing.
typedef void (^VoidBlock)(void);
/// Returns: true if the block throws an `NSException`, otherwise false
BOOL throwsToBool(VoidBlock block);
// ThrowsToBool.m
#import "ThrowsToBool.h"
BOOL throwsToBool(VoidBlock const block) {
#try {
block();
}
#catch (NSException * const notUsed) {
return YES;
}
return NO;
}
// xxxTests-Bridging-Header.h
#import "ThrowsToBool.h"
Then you can write:
XCTAssert(throwsToBool {
// test code that throws an NSException
})
But it doesn't work for assert or precondition :(
PS I got the idea from: http://modocache.io/xctest-the-good-parts

Answer 2

I think the assert()-function should only be used for debug-purposes. Not only because of the following statement from Apple's Swift-Book (https://itun.es/de/jEUH0.l):
„Assertions cause your app to terminate and are not a substitute for designing your code in such a way that invalid conditions are unlikely to arise.“
Thats why I would solve this as follows:
import Cocoa
import XCTest
class Square
{
let sideLength: Int
init(_ sideLength: Int)
{
self.sideLength = sideLength >= 0 ? sideLength : 0
}
}
class SquareTests: XCTestCase
{
override func setUp() { super.setUp() }
override func tearDown() { super.tearDown() }
func testMySquareSideLength() {
let square1 = Square(1);
XCTAssert(square1.sideLength == 1, "Sidelength should be 1")
let square2 = Square(-1);
XCTAssert(square2.sideLength >= 0, "Sidelength should be not negative")
}
}
let tester = SquareTests()
tester.testMySquareSideLength()

Answer 3

There is no equivalent to XCTAssertThrows in swift. For now you can't use a native function, but there is a solution with some objective-c help. You can use Quick, or only Nimble. Or to make your own assert function - see this article - http://modocache.io/xctest-the-good-parts - Potential Improvement #2: Add XCTAssertThrows to Swift

Answer 4

the best way is add a bridge I think.
please look at https://gist.github.com/akolov/8894408226dab48d3021
it works for me.

Answer 5

correct way in Swift 2:
class Square : NSObject{
let sideLength: Int
init(sideLength: Int) throws { // throwable initializer
guard sideLength >= 0 else { // use guard statement
throw ...// your custom error type
}
self.sideLength = sideLength
super.init()
}
}
and testing:
func testInitThrows() {
do {
_ = try Square(sideLength: -1) // or without parameter name depending on Swift version
XCTFail()
} catch ... { // your custom error type
} catch {
XCTFail()
}
}