How to test wether a function in Swift 2.0 throws or not? How to assert that the correct ErrorType
is thrown?
How to test wether a function in Swift 2.0 throws or not? How to assert that the correct ErrorType
is thrown?
EDIT: Updated the code for Swift 4.1
(still valid with Swift 5.2
)
Here's the latest Swift version of Fyodor Volchyok's answer who used XCTAssertThrowsError
:
enum MyError: Error {
case someExpectedError
case someUnexpectedError
}
func functionThatThrows() throws {
throw MyError.someExpectedError
}
func testFunctionThatThrows() {
XCTAssertThrowsError(try functionThatThrows()) { error in
XCTAssertEqual(error as! MyError, MyError.someExpectedError)
}
}
If your Error
enum has associated values, you can either have your Error
enum conform to Equatable
, or use the if case
statement:
enum MyError: Error, Equatable {
case someExpectedError
case someUnexpectedError
case associatedValueError(value: Int)
}
func functionThatThrows() throws {
throw MyError.associatedValueError(value: 10)
}
// Equatable pattern: simplest solution if you have a simple associated value that can be tested inside 1 XCTAssertEqual
func testFunctionThatThrows() {
XCTAssertThrowsError(try functionThatThrows()) { error in
XCTAssertEqual(error as! MyError, MyError.associatedValueError(value: 10))
}
}
// if case pattern: useful if you have one or more associated values more or less complex (struct, classes...)
func testFunctionThatThrows() {
XCTAssertThrowsError(try functionThatThrows()) { error in
guard case MyError.associatedValueError(let value) = error else {
return XCTFail()
}
XCTAssertEqual(value, 10)
// if you have several values or if they require more complex tests, you can do it here
}
}