gulp-spawn-mocha/README.md

Runs Mocha as a child process.

# gulp-spawn-mocha

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This is a plugin for [gulp] which runs [Mocha] tests in a separate process from
the `gulp` process. Each time tests are run a new child process is created
meaning the test environment always starts cleanly, i.e., globals are reset as
are non-enumerable properties defined on native prototypes via
`Object.defineProperty`. This also means that if your tests crash the node
process (e.g., `process.exit(-1)`.) then an `error` event is emitted rather than
your whole `gulp` process crashing (good for watching).

## Usage

Usage is according to this API:

```javascript
stream.pipe(
  mocha({
    // options
  })
);
```

This plugin uses `mocha` version `^6.0.0`. The major version of this plugin will
match the major version of `mocha`, which is a peer dependency of this plugin.

The plugin accepts these special options:

- `bin`: a path to a `mocha` executable to use instead of the one this plugin
  looks for by default. This is useful if you want to use a fork of `mocha`
  which goes by a different name or a different executable altogether.
- `env`: the environment variables that the child process will have access to
  (key-value pairs, see [child_process::fork][fork]). These variables are
  merged with your current environment variables and sent to the mocha
  executable.
- `cwd`: the working directory for the child process. This can be used to put
  files that the test creates or reads from the working directory in a specific
  directory, instead of the directory where you are running gulp from.
- `execPath`: an alternative execution path to the Node.js instance.
  If not specified, by default, [child_process::fork][fork] will spawn the new
  Node.js instances using the [process::execPath][execpath] of the parent process.

All other options are properly prefixed with either `-` or `--` and passed to
the `mocha` executable. Any arguments which do not take a value (e.g., `c`,
`colors`, or `debug`) should just have a value of `true`. Any arguments which
have dashes in the name can be specified by using camelCase (i.e., `debugBrk`
for `--debug-brk`, `inlineDiffs` for `--inline-diffs`, etc) so you don't have
to use strings for the argument names. Please note that the `gc` option must
be specified as `exposeGc` (please see [issue #21][21]). For an example, see
this plugin's very own `gulpfile.js`:

```javascript
const DEBUG = process.env.NODE_ENV === "debug",
  CI = process.env.CI === "true";

var gulp = require("gulp"),
  mocha = require("./lib");

gulp.task("test", function() {
  return gulp.src(["test/*.test.js"], { read: false }).pipe(
    mocha({
      debugBrk: DEBUG,
      r: "test/setup.js",
      R: CI ? "spec" : "nyan",
      istanbul: !DEBUG
    })
  );
});

gulp.task("default", ["test"], function() {
  gulp.watch("{lib,test}/*", ["test"]);
});
```

With this setup the `nyan` reporter will be used in development and the `spec`
reporter will be used in CI (Travis sets the `CI` environment variable to
`true` automatically).

The `default` task will execute tests and watch for changes and execute tests
whenever a change is detected.

### Conditional Arguments

If the value of an argument is falsy (but not `0`) then it will not be passed
to `mocha`. This is useful, for example, if you want to enable debugging only
when a certain environment variable is true. Example:

```javascript
const DEBUG = process.env.NODE_ENV === "debug";
stream.pipe(
  mocha({
    debugBrk: DEBUG,
    istanbul: !DEBUG
  })
);
```

### Custom Environment Variables

As mentioned above an object provided underneath the `env` options key will
allow you to specify a custom environment. This is useful, for example, to run
your tests in a different NODE_ENV than the default. Such a gulp task would
look like this:

```javascript
var gulp = require("gulp"),
  mocha = require("gulp-spawn-mocha");

gulp.task("test", function() {
  return gulp.src(["test/*.test.js"]).pipe(
    mocha({
      env: { NODE_ENV: "test" }
    })
  );
});
```

These variables are merged with your current environment variables and sent to
the mocha executable.

### Code Coverage

Because of the nature of this plugin launching an external process to run tests,
the standard coverage plugins for gulp will not work with this module. Starting
in version `0.4.0` [Istanbul] is included in order to enable code coverage
reports without having to instrument code on disk. You can use it by passing the
`istanbul` option.

Set `istanbul` to `true` if you want to use all the default settings:

```javascript
gulp.task("test", function() {
  return gulp.src(["test/*.test.js"]).pipe(
    mocha({
      istanbul: true
    })
  );
});
```

This will launch a process equivilant to:

```
istanbul cover -- _mocha
```

The default settings of Istanbul output to a directory in the `cwd` called
`coverage`.

If you want to pass options to Istanbul, you can do that as well:

```javascript
gulp.task("test", function() {
  return gulp.src(["test/*.test.js"]).pipe(
    mocha({
      istanbul: {
        dir: "path/to/custom/output/directory"
      }
    })
  );
});
```

This will launch a process equivilant to:

```
istanbul cover --dir path/to/custom/output/directory -- _mocha
```

This will output to a directory called `path/to/custom/output/directory`.

Istanbul, like `mocha`, supports a custom `bin` option so you can use a custom
fork of Istanbul:

```javascript
gulp.task("test", function() {
  return gulp.src(["test/*.test.js"]).pipe(
    mocha({
      istanbul: {
        dir: "path/to/custom/output/directory",
        bin: require.resolve("isparta") + "/bin/isparta"
      }
    })
  );
});
```

This will launch a process equivilant to:

```
./node_modules/isparta/bin/isparta cover --dir path/to/custom/output/directory -- _mocha
```

#### Publishing Coverage Reports

Assuming you are using [Travis] for CI and [Coveralls] for
publishing code coverage reports it is very easy to automatically have Travis
publish to Coveralls when tests are run successfully. First make sure you
install and save the `coveralls` module as a dev dependency:

```
npm i --save-dev coveralls
```

Then edit your `.travis.yml` to have an `after_success` command:

```yaml
language: node_js
node_js:
  - "0.11"
  - "0.10"
after_success: ./node_modules/.bin/coveralls --verbose < coverage/lcov.info
```

The `coveralls` module requires no additional configuration to publish to
Coveralls as long as both Travis and Coveralls are configured for the same
_public_ repository. See [`node-coveralls`][ncov] for more details.

### Output Reports to a File

You can pass `output` option to write a report to a writeable stream. If
`output` is a string then a writeable stream will be created with `output` as
its path. Note, if you are using `istanbul`, your reports content may contain
`istanbul`'s result.

Use file path:

```js
gulp.task("test", function() {
  return gulp.src(["test/*.test.js"], { read: false }).pipe(
    mocha({
      debugBrk: DEBUG,
      r: "test/setup.js",
      R: CI ? "spec" : "nyan",
      istanbul: !DEBUG,
      output: "result.log"
    })
  );
});
```

Use file stream:

```js
gulp.task("test", function() {
  return gulp.src(["test/*.test.js"], { read: false }).pipe(
    mocha({
      debugBrk: DEBUG,
      r: "test/setup.js",
      R: CI ? "spec" : "nyan",
      istanbul: !DEBUG,
      output: fs.createWriteStream("result.log", { flags: "w" })
    })
  );
});
```

## This or `gulp-mocha`?

The original `gulp-mocha` is fine in most circumstances. If you need your
tests to run as a separate process (or a separate process is simply your
preference for the reasons specified above) or you need to use a custom
version of Mocha (e.g., a fork with bug fixes or custom functionality) then
you should use this plugin.

## License

[**MIT**](./LICENSE)

[gulp]: http://gulpjs.com/ "gulp.js"
[mocha]: http://mochajs.org/ "Mocha"
[fork]: https://nodejs.org/api/child_process.html#child_process_child_process_fork_modulepath_args_options "child_process::fork"
[execpath]: https://nodejs.org/api/process.html#process_process_execpath "process::execPath"
[istanbul]: https://github.com/gotwarlost/istanbul "Istanbul"
[travis]: https://travis-ci.org/ "Travis CI"
[coveralls]: https://coveralls.io/ "Coveralls"
[ncov]: https://github.com/nickmerwin/node-coveralls "node-coveralls"
[21]: https://github.com/knpwrs/gulp-spawn-mocha/issues/21 "Issue 21: Setting `gc` option calls `mocha --gc` instead of `mocha -gc`"