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Merge pull request #15 from CodaFi/assertiveness-training
Assertive Properties
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@@ -17,3 +17,4 @@ DerivedData | |
| .idea/ | ||
| *.hmap | ||
| *.xcuserstate | ||
| Carthage/ | ||
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| //: ## SwiftCheck - noun: QuickCheck for Swift. | ||
| //: | ||
| //: SwiftCheck is a testing library that automatically generates random data for testing of program | ||
| //: properties. | ||
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| import SwiftCheck | ||
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| //: For example, if we wanted to test the property that every Integer is equal to itself, we would | ||
| //: express it as such and SwiftCheck will handle the rest: | ||
| property["Integer equality obeys reflexivity"] = forAll { (i : Int) in | ||
| return i == i | ||
| } | ||
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| //: ## Shrinking | ||
| //: What makes QuickCheck unique is the notion of shrinking test cases. When fuzz testing with | ||
| //: arbitrary data, rather than simply halt on a failing test, SwiftCheck will begin whittling the | ||
| //: data that causes the test to fail down to a minimal counterexample. | ||
| //: | ||
| //: For example, the following function uses the Sieve of Eratosthenes to generate a list of primes | ||
| //: less than some n: | ||
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| // The Sieve of Eratosthenes: | ||
| // | ||
| // To find all the prime numbers less than or equal to a given integer n: | ||
| // - let l = [2...n] | ||
| // - let p = 2 | ||
| // - for i in [(2 * p) through n by p] { | ||
| // mark l[i] | ||
| // } | ||
| // - Remaining indices of unmarked numbers are primes | ||
| func sieve(n : Int) -> [Int] { | ||
| if n <= 1 { | ||
| return [Int]() | ||
| } | ||
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| var marked : [Bool] = (0...n).map({ _ in false }) | ||
| marked[0] = true | ||
| marked[1] = true | ||
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| for p in 2..<n { | ||
| for i in stride(from: 2 * p, to: n, by: p) { | ||
| marked[i] = true | ||
| } | ||
| } | ||
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| var primes : [Int] = [] | ||
| for (t, i) in Zip2(marked, 0...n) { | ||
| if !t { | ||
| primes.append(i) | ||
| } | ||
| } | ||
| return primes | ||
| } | ||
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| // Trial Division | ||
| // | ||
| // Short and sweet check if a number is prime by enumerating from 2...⌈√(x)⌉ and checking | ||
| // for a nonzero modulus. | ||
| func isPrime(n : Int) -> Bool { | ||
| if n == 0 || n == 1 { | ||
| return false | ||
| } else if n == 2 { | ||
| return true | ||
| } | ||
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| let max = Int(ceil(sqrt(Double(n)))) | ||
| for i in 2...max { | ||
| if n % i == 0 { | ||
| return false | ||
| } | ||
| } | ||
| return true | ||
| } | ||
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| //: We would like to test whether our sieve works properly, so we run it through SwiftCheck with the | ||
| //: following property: | ||
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| property["All Prime"] = forAll { (n : Int) in | ||
| return sieve(n).filter(isPrime) == sieve(n) | ||
| } | ||
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| //: Which produces the following in our testing log: | ||
| //: | ||
| //: > Test Case '-[SwiftCheckTests.PrimeSpec testAll]' started. | ||
| //: > *** Failed! Falsifiable (after 10 tests): | ||
| //: > 4 | ||
| //: | ||
| //: Indicating that our sieve has failed on the input number 4. A quick look back at the comments | ||
| //: describing the sieve reveals the mistake immediately: | ||
| //: | ||
| //: > - for i in stride(from: 2 * p, to: n, by: p) { | ||
| //: > + for i in stride(from: 2 * p, through: n, by: p) { | ||
| //: | ||
| //: Running SwiftCheck again reports a successful sieve of all 100 random cases: | ||
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| func sieveProperly(n : Int) -> [Int] { | ||
| if n <= 1 { | ||
| return [Int]() | ||
| } | ||
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| var marked : [Bool] = (0...n).map({ _ in false }) | ||
| marked[0] = true | ||
| marked[1] = true | ||
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| for p in 2..<n { | ||
| for i in stride(from: 2 * p, through: n, by: p) { | ||
| marked[i] = true | ||
| } | ||
| } | ||
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| var primes : [Int] = [] | ||
| for (t, i) in Zip2(marked, 0...n) { | ||
| if !t { | ||
| primes.append(i) | ||
| } | ||
| } | ||
| return primes | ||
| } | ||
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| property["All Prime"] = forAll { (n : Int) in | ||
| return sieveProperly(n).filter(isPrime) == sieveProperly(n) | ||
| } |
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| // | ||
| // This file (and all other Swift source files in the Sources directory of this playground) will be precompiled into a framework which is automatically made available to SwiftCheck.playground. | ||
| // |
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| <?xml version="1.0" encoding="UTF-8" standalone="yes"?> | ||
| <playground version='5.0' target-platform='osx' display-mode='rendered'> | ||
| <timeline fileName='timeline.xctimeline'/> | ||
| </playground> |
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SwiftCheck/SwiftCheck.playground/playground.xcworkspace/contents.xcworkspacedata
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| <?xml version="1.0" encoding="UTF-8"?> | ||
| <Timeline | ||
| version = "3.0"> | ||
| <TimelineItems> | ||
| </TimelineItems> | ||
| </Timeline> |
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