Code coverage allows you to determine how well unit-tests cover your codebase. The standard code coverage suite for JavaScript is the NYC interface for Istanbul. However, this package doesn’t play well with NodeJS modules. Instead we are going to use the C8 package. C8 uses functionality native to NodeJS to create output that is compatible with Istanbul reporters.
Installation
npm i --save-dev c8Execution
You can run c8 on any source file by simply passing in the appropriate node command.
$ npx c8 node src/index.js
-----------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-----------|---------|----------|---------|---------|-------------------
All files | 88.23 | 100 | 50 | 88.23 |
MooYou.js | 84.61 | 100 | 50 | 84.61 | 9-10
index.js | 100 | 100 | 100 | 100 |
-----------|---------|----------|---------|---------|-------------------You can also easily run it with your Mocha test files.
$ npx c8 mocha
MooYou Class Test
#who
✔ returns 'you'
1 passing (3ms)
-----------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-----------|---------|----------|---------|---------|-------------------
All files | 84.61 | 100 | 50 | 84.61 |
MooYou.js | 84.61 | 100 | 50 | 84.61 | 9-10
-----------|---------|----------|---------|---------|-------------------Configuration
C8 can be configured from the command line, in your package.json file, or in a configuration file in your project directory. In particular you can instruct C8 to report one files as opposed to just those in your tests (npx c8 --all mocha). You can also specify which files to include and/or ignore. See the configuration documentation for specific details.
Generating Reports
By default the coverage data will be located in the coverage/tmp directory. You can change this directory with the --temp-directory.gitignore file.
Run npx c8 report to regenerate reports after c8 has already been run. Use the -r flag to specify which reporter to use, and the -o flag to specify where to output the report. By default generated reports can be found in the coverage/ dirctory.
Vanilla C8 command with HTML report:
npx c8 -r html mochaGenerate C8 report after the fact:
npx c8 -r html reportTwo-part C8 command with custom directories and HTML report:
npx c8 --temp-directory .c8 mocha
npx c8 report --temp-directory .c8 -o html_coverage -r htmlIn Code Markup
You can add comments into your source code that tells c8 to ignore certain portions of code.
Ignoring all lines until told to stop.
/* c8 ignore start */
function foo() {
...
}
/* c8 ignore stop */Ignore next line.
/* c8 ignore next */