Ensure annotations in code match actual coverage.
To install:
cargo install cargo-coverage-annotations
To run on a cargo project in the current working directory, first generate
cobertura.xml files(s) anywhere under the current working directory. This can
be done in one of way too many ways, as there's no standard rust cargo
coverage for now.
Two options I have tested and you might want to consider are:
cargo tarpaulin --out Xml will generate a single cobertura.xml file in the
top level directory. This is much simpler to use than kcov, without
requiring cargo make.
Note that as of version 0.5.5, tarpaulin is still not 100% reliable. This
might require you to insert spurious coverage annotations to the source code,
which defeats their purpose.
cargo make coverage will by default use kcov to generate several
cobertura.xml files nested in the bowels of target/coverage/.... This
requires installing cargo make, which I found to be more convenient than
trying to create the magical incantations for running kcov myself.
Note that cargo make version 0.7.11 insists all your files in the tests
directory be named test_*.rs, and that there will be at least one such test
file (in addition to any #[test] functions you might have in the sources).
Note that kcov, as of version 34, also returns wrong coverage results, at
least sometimes, at least for rust. It seems to be more robust than
tarpaulin, though.
To combat the flakiness in the coverage reporting tools, reported coverage is
ignored for lines that contain only \s*})*;? or only \s*} else {. This seems
to avoid the worst false coverage offenders; YMMV.
Of course, other tools generate other coverage file formats, and place them in different places. If you look at https://codecov.io/bash you will see >1K lines of code for detecting these files, and this doesn't cover the code for parsing the different formats. So, if your favorite tool isn't supported, don't be surprised, and pull requests are welcome ;-)
To verify that the coverage annotations in the code match the actual coverage,
run cargo coverage-annotations. This will merge the coverage information from
all the cobertura.xml files, and compare the results with the coverage
annotation comments (see below).
If you use cargo make, here is one way to
integrate cargo coverage-annotations into your workflow:
```toml [tasks.coverage-annotations-flow] description = "Runs the full coverage-annotations flow." dependencies = ["test", "coverage", "coverage-annotations"]
[tasks.coverage-annotations] description = "Verify the coverage annotations in the code" install_crate = "cargo-coverage-annotations" command = "cargo" args = ["coverage-annotations"]
[tasks.pre-coverage] run_task = "test"
[tasks.post-coverage] run_task = "coverage-annotations"
[tasks.post-test] run_task = "coverage-annotations-flow"
[tasks.format] dependencies = ["format-nightly"] ```
This will automatically verify the annotations in a new cargo make
coverage-annotations-flow, as well as as a part of cargo make
coverage-flow, and everything that invokes it (e.g., cargo make
dev-test-flow, cargo make build-flow, and cargo make ci-flow).
To keep your code base clean, it can be helpful to fail the CI build when the
code contains wrong coverage annotations. To achieve this, include cargo
coverage-annotations`` in your CI build steps. For example, a minimal Travis
setup usingtarpaulin` might look like this:
yaml
language: rust
cache: cargo
before_script:
- export PATH="$PATH:$HOME/.cargo/bin"
- which cargo-tarpaulin || cargo install cargo-tarpaulin
- which cargo-coverage-annotations || cargo install cargo-coverage-annotations
script:
- cargo build
- cargo test
- cargo tarpaulin --out Xml
- cargo coverage-annotations
Note that using cache: cargo is optional but highly recommended to speed up
the installation.
Coverage annotations are comments that indicate the coverage status of the code
lines. By default, code lines are assumed to be covered by tests. Lines
that are not tested are expected to end with an explicit // NOT TESTED comment.
It is also possible to mark a line with a // MAYBE TESTED comment in
special cases (for example, lines that only execute on some platforms).
Sometimes a whole block of lines needs to be marked. In this case, it is
possible to surround such lines with // BEGIN NOT TESTED ... // END NOT
TESTED comments (or // BEGIN MAYBE TESTED ... // END MAYBE TESTED).
Inside such regions, it is possible to override the annotation for specific
lines with // TESTED, // NOT TESTED or // MAYBE TESTED comments.
Finally, some files might not be tested at all. In this case, they must contain
in one of their lines a // FILE NOT TESTED or // FILE MAYBE TESTED comment.
This includes examples files.
Coverage annotations are only used for files in the src directory. They ensure
that when reading the code, one is aware of what is and is not covered by tests.
Of course, line coverage is only the most basic form of coverage tracking; that
said, tracking it at each step is surprisingly effective in isolating cases when
the code does not behave as expected.
cargo-coverage-annotations is distributed under the GNU General Public License
(Version 3.0). See the LICENSE for details.