Demonstration of assertion behaviour in different build modes

testingAssertions.swift

import Foundation

func testAssert(x:Int)->Int {
    var res = 0
    if x > 0 {
        res += 3
        
        assertionFailure("testAssert")
        res += 5
        return res
    } else {
        res += 7
    }
    
    res += 2
    return res
}


let i:Int = Int(arc4random())
print(i)

let result = testAssert(i)

print("\n")

print(result)

print("\n")
print("End")

// Result is:
// 1661870581 -- (random result will vary but will be +ve
// 9  -- (result of false case as assertion assumed valid in -Ounchecked in 6.4 or DISABLE_SAFETY_CHECKS in XC7
// End -- Reaches end of execution
// Program ended with exit code: 0 -- (Exits without error).

// For -O /safety checks on builds the 9 is replaced by 8 showing the test remains in place.