Add code coverage for tests

[zbraniecki]

It would help me to work with the parser tests to know how much of the parser is covered with tests. Istanbul seems like a good candidate? https://github.com/gotwarlost/istanbul

[stasm]

I tried running the following commands:

npm install istanbul
cd fluent
../node_modules/.bin/istanbul cover ../node_modules/.bin/_mocha -- -u tdd -r test/setup.js

which according to gotwarlost/istanbul#44 (comment) should work. Unfortunately I got:

No coverage information was collected, exit without writing coverage information

[stasm]

I'd like to have coverage reports as well. I'll try to get this working today or tomorrow.

[stasm]

Looks like npm installs istanbul v0.4.5 by default. Installing v1.1.0-alpha.1 fixes the above issue.

I managed to get coverage reports working for all packages except for fluent-syntax. I'm getting a weird ReferenceError: Function is not defined. I'll dig some more.

[Pike]

I'd argue that instanbul isn't a good candidate, looking at the state of releases that project had in the last year (effectively none, and it might be that 1.1.0 alpha 1 is actually older than 0.4.5)

[stasm]

Do you know any alternatives? I found blanket which isn't maintained anymore; the author recommends istanbul.

[stasm]

Istanbul is now maintained in https://github.com/istanbuljs and is at version 1.1.2. I gave it another try but ran into a coupe of issues:

• There's a bug in Istanbul which makes it crash when it sees the Function class in fluent-syntax/src/ast.js. We could possibly rename that class or exclude that file from the coverage report.

• The results for fluent/src/{parser,resolver}.js looks as if there was unclosed <span class="cstat-no"> element in the result: it's all red after a point.

@zbraniecki, I don't want to spend too much on this right now. I pushed my WIP branch to https://github.com/stasm/fluent.js/tree/istanbul. Feel free to take over if you have cycles for this.

[stasm]

One year and 12 major releases of istanbul later, creating coverage reports is as simple as running nyc mocha rather than mocha :) See #290.