Open Radar

 
When writing tests, I often have to create "mocks" of classes within my app. Mocking is a really common technique used in the Ruby and JavaScript communities but isn't used much in Swift or Objective-C. The most popular mocking library is open source: http://ocmock.org

So here's what I want from Xcode, out of the box: I want to be able to create mocks of a test subject's dependencies and use dependency injection to give them to the subject. Then I can run the code on the subject and assert that the mock received certain messages. It's cumbersome to describe a hypothetical syntax, so let me provide you with a few tests from a Ruby codebase I maintain.

it "handles swiftlint not being installed" do
  allow_any_instance_of(Swiftlint).to receive(:is_installed?).and_return(false)
  expect { @swiftlint.lint_files }.to raise_error("swiftlint is not installed")
end

it 'default config is nil, unspecified' do
  allow(@swiftlint.git).to receive(:added_files).and_return([])
  allow(@swiftlint.git).to receive(:modified_files).and_return([
    'spec/fixtures/SwiftFile.swift',
  ])

  expect_any_instance_of(Swiftlint).to receive(:lint)
    .with(hash_including(:config => nil), '')
    .once
    .and_return(@swiftlint_response)

  @swiftlint.lint_files
end

Equivalent tests written in vanilla XCTest are cumbersome, involve extensive subclassing and a tonne of boilerplate. The sad truth is: most developers don't write enough unit tests, and the lack of a decent, first-party mocking library would go a long way to improve this problem.

The static nature of Swift, and to some extent of Objective-C, make creating mocks a challenge. But I know you're up to it.