D3 Scatter Plot Tests

Here’s my project so far:

I have questions about the test errors I’m getting.

Regarding tests 7 and 8, can anyone give me some insight on why the error is "cannot read property ‘length’ of’null? My dots look to be positioned correctly with precision, but the test must be receiving the wrong type of data.

Regarding tests 9,10,11, and 12: It looks like these are failing because it is reading Y-axis data for the X-axis tests, and vice-versa. The errors are along the lines of ‘Expected 36:00 to equal 1999’, and this type of reversal is present on each test. I don’t see why the tests would be reversing the axes this way.