It is duplicated so we can make sure that the error message is correct. If someone makes a mistake in `cant_continue_mistake` the test will not catch the erroneous error message.

If it is not important to test the error message, we can change the test to not check it:
```elixir
assert_raise Mix.Error, fn ->
  Mix.Tasks.Deps.Check.run []
end
```

As it is now is sort of like checking that `foo() == foo()`.