How to unit test throwing functions in Swift?

Question

How to test wether a function in Swift 2.0 throws or not? How to assert that the correct ErrorType is thrown?

Answer 1

You can use this function:

func XCTAssertThrowsError(
  _ expression: @autoclosure () throws -> T,
  error: E,
  in file: StaticString = #file,
  line: UInt = #line
  ) {
  var thrownError: Error?
  XCTAssertThrowsError(
    try expression(),
    file: file,
    line: line) {
      thrownError = $0
  }

  XCTAssertTrue(
    thrownError is E,
    "Unexpected error type: \(type(of: thrownError))",
    file: file,
    line: line
  )

  XCTAssertEqual(
    thrownError as? E,
    error,
    file: file,
    line: line
  )
}

Example:

XCTAssertThrowsError(try funcThatThrowsSpecificError(), error: SpecificErrorEnum.someError)