Fix TTY color support

[na--]

This used to be considered a minor issue and lived as this code TODO: https://github.com/loadimpact/k6/blob/c00a85bfea21d748f0f9d11fdbc326087f34c411/cmd/root.go#L139-L154

But it turns out that the problem is a bit bigger than that, evidenced by my troubles with the recent summary work (After #1788, #1768, #1803). I noticed that in the above code, we don't even check for stdoutTTY or stderrTTY. Instead, we actually somewhat implement the TODO above, but in a nasty way that doesn't use dependency injection and is completely untestable...

The color library directly uses Go's os package to check things for itself: https://github.com/loadimpact/k6/blob/c00a85bfea21d748f0f9d11fdbc326087f34c411/vendor/github.com/fatih/color/color.go#L20-L21

And we also directly use stderrTTY in our logger constructor: https://github.com/loadimpact/k6/blob/c00a85bfea21d748f0f9d11fdbc326087f34c411/cmd/root.go#L309

And for a taste of #883, nocolor, stdoutTTY, and stderrTTY are all global variables... 😭 So yeah, all of these things get in the way of handling colors in the JS-based summary handlers properly...

[na--]

Somewhat connected issue: #1748

[mstoykov]

I am sometimes (rarely) getting

--- FAIL: TestExceptionInHandleSummaryFallsBackToTextSummary (0.00s)
        Error Trace:    summary_test.go:470
        Error:          "
                             █ child

                               ✓ check1
                               ✗ check3
                                ↳  66% — ✓ 10 / ✗ 5
                               ✗ check2
                                ↳  33% — ✓ 5 / ✗ 10

                           ✓ checks......: 75.00% ✓ 45  ✗ 15
                           ✗ http_reqs...: 3      3/s
                           ✗ my_trend....:
                             vus.........: 1      min=1 max=1

                        " does not contain "     █ child

                               ✓ check1
                               ✗ check3
                                ↳  66% — ✓ 10 / ✗ 5
                               ✗ check2
                                ↳  33% — ✓ 5 / ✗ 10

                           ✓ checks......: 75.00% ✓ 45  ✗ 15
                           ✗ http_reqs...: 3      3/s
                        "
        Test:           TestExceptionInHandleSummaryFallsBackToTextSummary
--- FAIL: TestTextSummary (0.00s)
    --- FAIL: TestTextSummary/0_[avg_min_med_max_p(90)_p(95)_p(99.9)] (0.00s)
        Error Trace:    summary_test.go:93
        Error:          Not equal:
                        expected: "\n     █ child\n\n       ✓ check1\n       ✗ check3\n        ↳  66% — ✓ 10 / ✗ 5\n       ✗ check2\n        ↳  33% — ✓ 5 / ✗ 10\n\n   ✓ checks......: 75.00% ✓ 45  ✗ 15 \n   ✗ http_reqs...: 3      3/s\n   ✗ my_trend....: avg=15ms min=10ms med=15ms max=20ms p(90)=19ms p(95)=19.5ms p(99.9)=19.99ms\n     vus.........: 1      min=1 max=1\n\n"
                        actual  : "\n     █ child\n\n\x1b[32m       ✓ check1\n\x1b[0m\x1b[31m       ✗ check3\n\x1b[0m\x1b[31m        ↳  66% — ✓ 10 / ✗ 5\n\x1b[0m\x1b[31m       ✗ check2\n\x1b[0m\x1b[31m        ↳  33% — ✓ 5 / ✗ 10\n\x1b[0m\n   \x1b[32m✓\x1b[0m checks\x1b[2m......:\x1b[0m \x1b[36m75.00%\x1b[0m \x1b[36;2m\x1b[36;2m✓ 45\x1b[0m  \x1b[36;2m✗ 15\x1b[0m \x1b[0m\n   \x1b[31m✗\x1b[0m http_reqs\x1b[2m...:\x1b[0m \x1b[36m3\x1b[0m      \x1b[36;2m3/s\x1b[0m\n   \x1b[31m✗\x1b[0m my_trend\x1b[2m....:\x1b[0m avg=\x1b[36m15ms\x1b[0m min=\x1b[36m10ms\x1b[0m med=\x1b[36m15ms\x1b[0m max=\x1b[36m20ms\x1b[0m p(90)=\x1b[36m19ms\x1b[0m p(95)=\x1b[36m19.5ms\x1b[0m p(99.9)=\x1b[36m19.99ms\x1b[0m\n   \x1b[m \x1b[0m vus\x1b[2m.........:\x1b[0m \x1b[36m1\x1b[0m      \x1b[36;2m\x1b[36;2mmin=1\x1b[0m \x1b[36;2mmax=1\x1b[0m\x1b[0m\n\n"
        Test:           TestTextSummary/0_[avg_min_med_max_p(90)_p(95)_p(99.9)]
    --- FAIL: TestTextSummary/2_[avg_count] (0.00s)
        Error Trace:    summary_test.go:93
        Error:          Not equal:
                        expected: "\n     █ child\n\n       ✓ check1\n       ✗ check3\n        ↳  66% — ✓ 10 / ✗ 5\n       ✗ check2\n        ↳  33% — ✓ 5 / ✗ 10\n\n   ✓ checks......: 75.00% ✓ 45  ✗ 15 \n   ✗ http_reqs...: 3      3/s\n   ✗ my_trend....: avg=15ms count=3\n     vus.........: 1      min=1 max=1\n\n"
                        actual  : "\n     █ child\n\n\x1b[32m       ✓ check1\n\x1b[0m\x1b[31m       ✗ check3\n\x1b[0m\x1b[31m        ↳  66% — ✓ 10 / ✗ 5\n\x1b[0m\x1b[31m       ✗ check2\n\x1b[0m\x1b[31m        ↳  33% — ✓ 5 / ✗ 10\n\x1b[0m\n   \x1b[32m✓\x1b[0m checks\x1b[2m......:\x1b[0m \x1b[36m75.00%\x1b[0m \x1b[36;2m\x1b[36;2m✓ 45\x1b[0m  \x1b[36;2m✗ 15\x1b[0m \x1b[0m\n   \x1b[31m✗\x1b[0m http_reqs\x1b[2m...:\x1b[0m \x1b[36m3\x1b[0m      \x1b[36;2m3/s\x1b[0m\n   \x1b[31m✗\x1b[0m my_trend\x1b[2m....:\x1b[0m avg=\x1b[36m15ms\x1b[0m count=\x1b[36m3\x1b[0m\n   \x1b[m \x1b[0m vus\x1b[2m.........:\x1b[0m \x1b[36m1\x1b[0m      \x1b[36;2m\x1b[36;2mmin=1\x1b[0m \x1b[36;2mmax=1\x1b[0m\x1b[0m\n\n"
        Test:           TestTextSummary/2_[avg_count]
    --- FAIL: TestTextSummary/1_[count] (0.00s)
        Error Trace:    summary_test.go:93
        Error:          Not equal:
                        expected: "\n     █ child\n\n       ✓ check1\n       ✗ check3\n        ↳  66% — ✓ 10 / ✗ 5\n       ✗ check2\n        ↳  33% — ✓ 5 / ✗ 10\n\n   ✓ checks......: 75.00% ✓ 45  ✗ 15 \n   ✗ http_reqs...: 3      3/s\n   ✗ my_trend....: count=3\n     vus.........: 1      min=1 max=1\n\n"
                        actual  : "\n     █ child\n\n\x1b[32m       ✓ check1\n\x1b[0m\x1b[31m       ✗ check3\n\x1b[0m\x1b[31m        ↳  66% — ✓ 10 / ✗ 5\n\x1b[0m\x1b[31m       ✗ check2\n\x1b[0m\x1b[31m        ↳  33% — ✓ 5 / ✗ 10\n\x1b[0m\n   \x1b[32m✓\x1b[0m checks\x1b[2m......:\x1b[0m \x1b[36m75.00%\x1b[0m \x1b[36;2m\x1b[36;2m✓ 45\x1b[0m  \x1b[36;2m✗ 15\x1b[0m \x1b[0m\n   \x1b[31m✗\x1b[0m http_reqs\x1b[2m...:\x1b[0m \x1b[36m3\x1b[0m      \x1b[36;2m3/s\x1b[0m\n   \x1b[31m✗\x1b[0m my_trend\x1b[2m....:\x1b[0m count=\x1b[36m3\x1b[0m\n   \x1b[m \x1b[0m vus\x1b[2m.........:\x1b[0m \x1b[36m1\x1b[0m      \x1b[36;2m\x1b[36;2mmin=1\x1b[0m \x1b[36;2mmax=1\x1b[0m\x1b[0m\n\n"
        Test:           TestTextSummary/1_[count]
FAIL
exit status 1

Where there is actually colors in the first part of the first error, but not the second. This seems to be confirmed by the lack of the coloring "characters" in the other errors. So it seems to me like something disables to colors? probably another test ... no idea 🤷

Also a picture of what I mean by "there is actually colors":

[na--]

Found something that might be useful on HN: https://notes.burke.libbey.me/ansi-escape-codes/ (https://news.ycombinator.com/item?id=26011198)

[na--]

Closed by #1975