Week 1: Unit Testing Assertions Cheat Sheet in Swift
Building apps is hard, and it’s even harder to debug. Since Xcode 5.0, Apple introduced the XCTest framework, which allows developers to build test automation for apps. Unit Testing automates the testing process, catches errors before the apps run, and saves developers a lot of time. In this story, let’s talk about all the assertions that are available for writing Unit Tests.
XCTAssert(expression: Bool)
This function generates success when the expression is true.
func testAssertion() {
let number = 2 XCTAssert(number > 1) // success
XCTAssert(number == 1) // failure
}XCTAssertTrue(expression: Bool)
This function is very similar to the XCTAssert(expression: Bool), it generates success when the expression is true.
func testAssertion() {
let number = 2 XCTAssertTrue(number > 1) // success
XCTAssertTrue(number == 1) // failure
}XCTAssertFalse(expression: Bool)
This function is the opposite of the XCTAssertTrue(expression: Bool) , it generates failure when the expression is true.
func testAssertion() {
let number = 2 XCTAssertFalse(number > 1) // failure
XCTAssertFalse(number == 1) // success
}XCTAssertNil(expression: Any?)
This function generates success when the expression is nil .
func testAssertion() {
let name: String? = nil
let number = 2 XCTAssertNil(name) // success
XCTAssertNil(number) // failure
}XCTAssertNotNil(expression: Any?)
This function is the opposite of the XCTAssertNil(expression: Any?) , it generates failure when the expression is nil.
func testAssertion() {
let name: String? = nil
let number = 2 XCTAssertNotNil(name) // failure
XCTAssertNotNil(number) // success
}XCTAssertEqual(expression1: Equatable, expression2: Equatable)
This function generates success when the both expressions are equal.
func testAssertion() {
let number = 2 XCTAssertEqual(number, 2) // success
XCTAssertEqual(number, 1) // failure
}XCTAssertNotEqual(expression1: Equatable, expression2: Equatable)
This function is the opposite of the XCTAssertEqual(expression1: Equatable, expression2: Equatable), it generates success when the both expressions are NOT equal.
func testAssertion() {
let number = 2 XCTAssertNotEqual(number, 1) // success
XCTAssertNotEqual(number, 2) // failure
}XCTAssertEqual(expression1: FloatingPoint, expression2: FloatingPoint, accuracy: FloatingPoint)
This function is similar to XCTAssertEqual(expression1: Equatable, expression2: Equatable) , but it compares two FloatingPoints with an accuracy.
func testAssertion() {
let number = 2 XCTAssertEqual(0.01, 0.02, accuracy: 0.01) // success
XCTAssertEqual(0.01, 0.02, accuracy: 0.001) // failure
}XCTAssertNotEqual(expression1: FloatingPoint, expression2: FloatingPoint, accuracy: FloatingPoint)
This function is the opposite of XCTAssertEqual(expression1: FloatingPoint, expression2: FloatingPoint, accuracy: FloatingPoint) , it compares two FloatingPoints with an accuracy. But it generates success when they are NOT equal.
func testAssertion() {
let number = 2 XCTAssertNotEqual(0.01, 0.02, accuracy: 0.001) // success
XCTAssertNotEqual(0.01, 0.02, accuracy: 0.01) // failure
}XCTAssertLessThan(expression1: Comparable, expression2: Comparable)
This function generates success when the expression1 is less than the expression2.
func testAssertion() {
let number = 2 XCTAssertLessThan(number, 3) // success
XCTAssertLessThan(number, 1) // failure
}XCTAssertGreaterThan(expression1: Comparable, expression2: Comparable)
This function is the opposite of XCTAssertLessThan(expression1: Comparable, expression2: Comparable) , it generates success when the expression1 is greater than the expression2.
func testAssertion() {
let number = 2 XCTAssertGreaterThan(number, 1) // success
XCTAssertGreaterThan(number, 3) // failure
}XCTAssertLessThanOrEqual(expression1: Comparable, expression2: Comparable)
This function generates success when the expression1 is less than or equal to the expression2.
func testAssertion() {
let number = 2 XCTAssertLessThan(number, 3) // success
XCTAssertLessThan(number, 2) // success
XCTAssertLessThan(number, 1) // failure
}XCTAssertGreaterThanOrEqual(expression1: Comparable, expression2: Comparable)
This function is the opposite of XCTAssertLessThan(expression1: Comparable, expression2: Comparable) , it generates success when the expression1 is greater than or equal to the expression2.
func testAssertion() {
let number = 2 XCTAssertGreaterThanOrEqual(number, 1) // success
XCTAssertGreaterThanOrEqual(number, 2) // success
XCTAssertGreaterThanOrEqual(number, 3) // failure
}XCTAssertNoThrow(expression: T)
This function generates success if the expression doesn't throw errors.
struct User: Decodable {
let firstname: String
let lastname: String
let age: Int
}func testAssertion() {
let JSONOne = """
{
"firstname": "Dylan",
"lastname": "Chen",
"age": 28
}
"""
let JSONTwo = """
{
"firstname": "Dylan",
"lastname": "Chen",
"age": "28"
}
""" let jsonDataOne = JSONOne.data(using: .utf8)!
let jsonDataTwo = JSONTwo.data(using: .utf8)!
XCTAssertNoThrow(try JSONDecoder().decode(User.self, from: jsonDataOne)) // Success XCTAssertNoThrow(try JSONDecoder().decode(User.self, from: jsonDataTwo)) // Failure, because "age" is supposed to be an integer.
}XCTAssertThrowsError(expression: T)
This function is the opposite of the XCTAssertNoThrow(expression: T) , it generates success when the expression throws errors.
struct User: Decodable {
let firstname: String
let lastname: String
let age: Int
}func testAssertion() {
let JSONOne = """
{
"firstname": "Dylan",
"lastname": "Chen",
"age": 28
}
"""
let JSONTwo = """
{
"firstname": "Dylan",
"lastname": "Chen",
"age": "28"
}
""" let jsonDataOne = JSONOne.data(using: .utf8)!
let jsonDataTwo = JSONTwo.data(using: .utf8)!
XCTAssertNoThrow(try JSONDecoder().decode(User.self, from: jsonDataOne)) // Failure XCTAssertNoThrow(try JSONDecoder().decode(User.self, from: jsonDataTwo)) // Success because "age" is supposed to be an integer.
}XCTAssertThrowsError(expression: T, message: String, errorHandler: (Error) -> Void)
This function is similar to XCTAssertThrowsError(expression: T) , in addition, the errorHandler allows us to catch the error and perform additional testing.
struct User: Decodable {
let firstname: String
let lastname: String
let age: Int
}func testAssertion() {
let JSON = """
{
"firstname": "Dylan",
"lastname": "Chen",
"age": "28"
}
""" let jsonData = JSON.data(using: .utf8)!
XCTAssertThrowsError(try JSONDecoder().decode(User.self, from: jsonData), "") { (error) in
print(error.localizedDescription) // The data couldn’t be read because it isn’t in the correct format.
} // failure
}All these assertion functions accept an optional argument message that customs the error description. For example,
XCTAssert(expression: Bool, message: String)
func testAssertion() {
let number = 2 XCTAssert(number == 1, "Number does NOT equal to 1 :)")
// failure, description: "Number does NOT equal to 1 :)"XCTAssert(number == 1)
// failure, description: "Test Case failed"
}
