Modules that include the EUnit header get an implicit test/0 fun,
which cover considers a runnable line, but eunit:(TestRepresentation)
never calls. Result: prod modules with tests can never reach 100%
coverage. Ironic. In this case, fix it by decrementing the NotCovered
counter returned by cover:analyze/3.
1. When running the eunit command with the convention of putting
tests in "*_tests" modules, eunit would run those tests twice. This
is because: 1) eunit:test/1 will naturally look for foo's tests both
in foo, and in foo_tests, and 2) eunit:test/1 was being folded over
all project modules. The fix is to filter "*_tests" modules from the
list passed to eunit:test/1.
2. When running the eunit command with cover enabled and tests in a
'test' directory, cover would error because it couldn't find the
source code for those tests. This is because cover:analyze/3 will
only find module source in "." and "../src". This is hard-coded in
cover :-(. Since cover shouldn't be calculating code coverage on test
code anyway, the fix is to not fold cover:analyze/3 over
non-production code.
3. When running the eunit command with cover enabled and a test suite
defined, cover would only attempt to calculate coverage on the the
test suite itself. This was because only the suite was passed to
cover:analyze/3. The fix is to fold cover:analyze/3 over all the
production code, filtering out the suite module if it is defined.
