es6-rewire-nyc

Small repo to simulate issue with istanbul/nyc and rewire

With rewire/cross-env

Running the test using the default commands (that use rewire and cross-env) will generate an empty coverage report:

npm run test

this command will execute only the tests and both of them will pass

npm run test:cov

this will execute the previous test script but will add the coverage report, which will result empty

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |        0 |        0 |        0 |        0 |                   |
----------|----------|----------|----------|----------|-------------------|

Without rewire/cross-env

removing cross-env NODE_ENV=test from the test script will avoid to load rewire and will generate a correct coverage. The side effect is that the test that use the rewire will fail.

npm run test2

will run the script without cross-env, so babel will not load the rewire plugin and so one test will fail.

npm run test:cov2

this command will use the previous test2 script and generate the coverage. In this case the coverage report will be generated correctly.

------------------|----------|----------|----------|----------|-------------------|
File              |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
------------------|----------|----------|----------|----------|-------------------|
All files         |    64.29 |      100 |    54.55 |    66.67 |                   |
 src              |       75 |      100 |       60 |    85.71 |                   |
  a-dependency.js |      100 |      100 |      100 |      100 |                   |
  a-module.js     |       60 |      100 |        0 |       75 |                 6 |
 tests            |       60 |      100 |       50 |       60 |                   |
  test.js         |       60 |      100 |       50 |       60 |... 23,24,26,27,28 |
------------------|----------|----------|----------|----------|-------------------|

but its not correct due the missing rewire plugin.

babelrc (es2015)

{
  "presets": ["es2015"],
  "env": {
    "test": {
      "plugins": ["istanbul", "rewire"]
    }
  }
}

this is the babel configuration file used in the solution. Removing rewire plugin from the plugin collection will generate and empty coverage with npm run test:cov but not with npm run test:cov2 (which is not using cross-env).

If I modify the babelrc in this way

{
  "presets": ["es2015"],
  "plugins": ["istanbul", "rewire"]
}

both npm run test:cov (with cross-env) and npm run test:cov2 (without cross-env). Will generate an empty result.

If I remove both the plugins

{
  "presets": ["es2015"]
}

both command (with and without cross-env) will generate a coverage result (partial, since one test will fail)

Removing only istanbul from the plugin collection will generate a full coverage file and this would be the result (as expected)

------------------|----------|----------|----------|----------|-------------------|
File              |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
------------------|----------|----------|----------|----------|-------------------|
All files         |      100 |      100 |      100 |      100 |                   |
 src              |      100 |      100 |      100 |      100 |                   |
  a-dependency.js |      100 |      100 |      100 |      100 |                   |
  a-module.js     |      100 |      100 |      100 |      100 |                   |
 tests            |      100 |      100 |      100 |      100 |                   |
  test.js         |      100 |      100 |      100 |      100 |                   |
------------------|----------|----------|----------|----------|-------------------|

babelrc (env)

After going across this issues around the previous es2015 preset, I moved to the env one. Installing it with npm install babel-preset-env --save-dev then I've modified my babelrc in this way.

{
  "presets": [
    ["env", {
      "targets": {
        "node": "current"
      }
    }]
  ],
  "env": {
    "test": {
      "plugins": ["istanbul", "rewire"]
    }
  }
}

In this case npm run test works properly and npm run test:cov will generate a correct coverage report. And there will be no issue with cross-end or rewire.

conclusion

Somehow both rewire and cross-env are creating issue if combined with babel when using the es2015 preset. To generate the report with this preset apparenttly is sufficient to remove istanbul from the babel plugins and use only rewire (it will work well also with cross-env in this case).

I rather suggest to upgrate to the env preset and use the babel plugins as suggested (unless it create other issue to your project)

env

> node --version
v9.4.0
> npm --version
5.6.0
>ver
Microsoft Windows [Version 10.0.16299.309]

Same behavior has been observed on MacOS