Counting unique values in y axis of a line/bar visualization

Hi there!

I'm trying to create a line/bar visualization based upon a query which returns all tests I run on my system. The main goal is to show a count of unique test titles on the Y axis (since some tests run several times a day, and I only need to which ran that day, not how many times), while the x axis is date histogram with a day interval and split series of the test titles.
The visualization shows all of the tests which ran that day. Looks like this:

What am I doing wrong?