There isn't much point to giving announced quizzes, exams, tests, whatever in foreign language classes. If you are after fluency, you'll agree we should only care about what the students have acquired, not what they've memorized. (The same might be true in other subjects, too, but I won't go there.)
If you announce that on Friday there will be a test, the students will go home and (if you're lucky) study and memorize. Then on the test they will regurgitate.
Announcing assessments makes the whole thing about assessments. "We need to prepare for the test next week, that looming, dark thing" or "This will be on the test, so you better pay attention!" Of course assessment are necessary, but don't give them so much attention. Use them as a tool to tell where you're students are at, not as an end in themselves.
My students know to expect a "quick quiz" at the end of most class periods, but beyond that I try not to advertise assessments. I've heard whispers that we "don't even take tests in that class!" Of course that's ridiculous. My students take a variety of assessments, I just don't tell them that's what they're doing. I might give them questions and say "answer these," or I say "write about this," or maybe "draw pictures of this," all casually so that students simply do the task without really thinking about it as a test.