Currently the test trend chart will interpolate results, using the most recent result it can find, smeared out up until the current day.
We run tests every night, and it would be good if the test trend chart correctly shows when the run did not work. Currently, if our test suite doesn't run, the the test trend chart makes it look like everything is identical to yesterday, when in fact, it isn't.
Perhaps there could be some setting somewhere to allow you to choose between the two behaviours:
1) The test trend chart will display the most recent result for each day until there is a new result. (current behaviour)
2) the test trend chart will show the actual result of each day. If there is no result for a given day, then the test trend chart will read zero for that day.