`--fail-under X` where X > 0 should pass on files with no statements

[CobaltCause]

Describe the bug
If I have a file with no statements, coverage report correctly says that the coverage is 100%. However, coverage report --fail-under 100 will fail because it thinks the coverage is 0%.

To Reproduce

1. Use Python 3.10
2. Use Coverage 6.4.4 with C extension

$ touch test.py
$ coverage run test.py
$ coverage report
Name      Stmts   Miss  Cover
-----------------------------
test.py       0      0   100%
-----------------------------
TOTAL         0      0   100%
$ echo $?
0
$ coverage report --fail-under 100
Name      Stmts   Miss  Cover
-----------------------------
test.py       0      0   100%
-----------------------------
TOTAL         0      0   100%
Coverage failure: total of 0 is less than fail-under=100
$ echo $?
2

Expected behavior
I would expect this to succeed with no error, it says right above that the coverage is 100%, but then claims it's 0% when --fail-under is supplied.

[nedbat]

Hmm, I see your point! For some reason, seven years ago in d20a77c, we added a test specifically to check that an empty file would fail-under=99. Maybe the behavior of empty files has changed since then? Was it 0% back then?

[CobaltCause]

A mystery. One other thing to point out, since it's only in the title, is that this happens with any value for fail-under greater than zero. For example, coverage report --fail-under 1 also causes coverage to exit with code 2.

[nedbat]

This is now fixed in commit d5c3daa.

[nedbat]

This is now released as part of coverage 7.0.0b1.