Swift testing non-scalar types - swift

Question

I want to test my function that takes a string, a returns all the pairs of characters as an array s.t.
func pairsOfChars(_ s: String) -> [(Character,Character)] {
let strArray = Array(s)
var outputArray = [(Character,Character)]()
for i in 0..<strArray.count - 1 {
for j in i + 1..<strArray.count {
outputArray.append( (strArray[i], strArray[j]) )
}
}
return outputArray
}
So I want to create a suite of tests using XCTestCase. I usually use XCTestCase and XCTAssertEqual but these are only appropriate for C scalar types. This means that the following test case returns an error:
class pairsTests: XCTestCase {
func testNaive() {
measure {
XCTAssertEqual( pairsOfChars("abc") , [(Character("a"),Character("b")),(Character("a"),Character("c")),(Character("b"),Character("c")) ] )
}
}
}
I could convert to a string, but I'm thinking there is a better solution.
How can I test an output of an array of pairs of characters [(Character,Character)]

Answer 1

Your notion of a nonscalar is a total red herring. The problem is one of equatability.
How can I test an output of an array of pairs of characters [(Character,Character)]
You can't, because there is no default notion of what it would mean to equate two such arrays. This is the old "tuples of Equatable are not Equatable" problem (https://bugs.swift.org/browse/SR-1222) which still rears its head with arrays. The == operator works on tuples by a kind of magic, but they are still not formally Equatable.
You could define equatability of arrays of character pairs yourself:
typealias CharPair = (Character,Character)
func ==(lhs:[CharPair], rhs:[CharPair]) -> Bool {
if lhs.count != rhs.count {
return false
}
let zipped = zip(lhs,rhs)
return zipped.allSatisfy{$0 == $1}
}
Alternatively, have your pairsOfChars return something that is more easily made equatable, such as an array of a struct for which Equatable is defined.
For example:
struct CharacterPair : Equatable {
let c1:Character
let c2:Character
// in Swift 4.2 this next bit is not needed
static func ==(lhs:CharacterPair, rhs:CharacterPair) -> Bool {
return lhs.c1 == rhs.c1 && lhs.c2 == rhs.c2
}
}
func pairsOfChars(_ s: String) -> [CharacterPair] {
let strArray = Array(s)
var outputArray = [CharacterPair]()
for i in 0..<strArray.count - 1 {
for j in i + 1..<strArray.count {
outputArray.append(CharacterPair(c1:strArray[i],c2:strArray[j]))
}
}
return outputArray
}
You would then rewrite the test to match:
XCTAssertEqual(
pairsOfChars("abc"),
[CharacterPair(c1:Character("a"),c2:Character("b")),
CharacterPair(c1:Character("a"),c2:Character("c")),
CharacterPair(c1:Character("b"),c2:Character("c"))]
)