Use short labels for the legend tests so as not to be affected by the font width

[nagix]

This fixes the #5816 test failures that can happen depending on environments.

[simonbrunel]

I still have one failing test :\

Firefox 63.0.0 (Windows 10.0.0) Legend block tests should draw correctly when the legend is positioned on the top FAILED
        Expected 105 to be close to pixel 107.
        @test/specs/plugin.legend.tests.js:213:48
        @test/specs/plugin.legend.tests.js:211:5
Chrome 70.0.3538 (Windows 10.0.0): Executed 759 of 763 (skipped 4) SUCCESS (4.835 secs / 4.629 secs)
Firefox 63.0.0 (Windows 10.0.0): Executed 535 of 763 (1 FAILED) (skipped 4) (0 secs / 4.832 secs)
Firefox 63.0.0 (Windows 10.0.0) Legend block tests should draw correctly when the legend is positioned on the top FAILED
        Expected 105 to be close to pixel 107.
Chrome 70.0.3538 (Windows 10.0.0): Executed 759 of 763 (skipped 4) SUCCESS (4.835 secs / 4.629 secs)
Firefox 63.0.0 (Windows 10.0.0): Executed 759 of 763 (1 FAILED) (skipped 4) (6.886 secs / 6.609 secs)
TOTAL: 1 FAILED, 1517 SUCCESS

[nagix]

All the text labels for the label box position tests are changed to empty. @simonbrunel Can you test again?

[simonbrunel]

It works, are these tests still pertinent without labels?

[nagix]

Well, they test the sizes and positions of legendHitBoxes which consist of a sample box + a padding area + a text label box. If we check if the size of the text label box is reflected in legendHitBoxes, would it be better to use some simple string like ' '?

[simonbrunel]

I think it will be the same issue with ' ' but we can try (though, that's weird it doesn't generate the same width for a space character). We can also try to use a more basic / common / generic font family in our tests (e.g. 'Arial'). Default is 'Helvetica Neue', 'Helvetica', 'Arial', sans-serif but I'm on Windows and don't have Helvetica Neue or Helvetica installed.

[nagix]

I tried Arial with different browsers on both Mac and Windows, but the results are not consistent at all (reference). Eventually, I reverted the changes in labels and added some adjustment to pixel values so that differences across environments stay within the margin range (+/-2).

[nagix]

It was passed on Mac and Windows, but still fails on Linux.

[nagix]

Now all the test passed. The results were more consistent when ' ' is used for labels.

[simonbrunel]

Thanks @nagix, it passes on my machine now.