Dictation
Hear a sentence, write it down. Spelling, vocabulary and grammar at once.
Dictation is the most honest test there is. You cannot guess from a written prompt, you cannot pattern-match — you have to actually recognise the words and know how they are spelled.
Listen as many times as you like. The replay button is not cheating; hearing the same sentence five times is exactly how the sounds start separating into words.
Things to listen for: the difference between der / die / das / dem / den, whether a verb has an umlaut (fährt, nicht fahrt), and any little word stranded at the end of the sentence.
Punctuation and capitalisation are graded gently — but a wrong article or a missing umlaut is a real mistake and will be pointed out.
If your device has no German voice installed, these exercises are hidden automatically rather than served in silence.