I am currently, and belatedly, getting on with the business of the literacy tests I am marking, using an instrument I adapted from an online test some years ago. The test very clearly highlights problems second-language English learners may present, but even native speakers rarely score 100%. It is in two parts: a multiple choice test that targets particular aspects of grammar, and a writing task that requires deployment, among other things, of just about the full range of tense and modality.
If you are curious, you can try it for yourselves. The test and answers are in a password-protected file, and yes, you may ask for the password via the contact page. Occasionally more than one answer is right in the multiple choice section.
I have administered this test, or its earlier versions, to over 1,500 students in the past decade.