Allow tests to tamper with Node.js built-ins without breaking AVA

[sindresorhus]

With latest master (c01ac05) and Node.js 4 and 7.

import fs from 'fs';
import test from 'ava';
import sinon from 'sinon';

test(t => {
	fs.readFileSync = sinon.stub(fs, 'readFileSync');
	// ...
	fs.readFileSync.restore();
	t.pass();
});

  2 exceptions

  Uncaught Exception
  TypeError: Cannot read property 'sections' of undefined
    new SourceMapConsumer (/Users/sindresorhus/dev/ava/node_modules/source-map/lib/source-map-consumer.js:20:19)
    mapSourcePosition (/Users/sindresorhus/dev/ava/node_modules/source-map-support/source-map-support.js:171:14)
    wrapCallSite (/Users/sindresorhus/dev/ava/node_modules/source-map-support/source-map-support.js:338:20)
    /Users/sindresorhus/dev/ava/node_modules/source-map-support/source-map-support.js:373:26
    Function.prepareStackTrace (/Users/sindresorhus/dev/ava/node_modules/source-map-support/source-map-support.js:372:24)

  ✖ Test results were not received from test.js

I think we need to protect all builtins from being overridden, so mocking in the tests doesn't affect our usage or our dependencies' usage of core APIs. Maybe running the test files in a new vm context would help with that?

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[sindresorhus]

Same without Sinon actually:

import fs from 'fs';
import test from 'ava';

test(t => {
	const _ = fs.readFileSync;
	fs.readFileSync = () => 'foo';
	const isFoo = require('.');
	fs.readFileSync = _;
	t.true(isFoo);
});

  2 exceptions

  Uncaught Exception
  SyntaxError: Unexpected token L in JSON at position 0
    SyntaxError: Unexpected token L in JSON at position 0
        JSON.parse (<anonymous>)
        new SourceMapConsumer (node_modules/source-map/lib/source-map-consumer.js:17:22)
        mapSourcePosition (node_modules/source-map-support/source-map-support.js:171:14)
        wrapCallSite (node_modules/source-map-support/source-map-support.js:338:20)
        node_modules/source-map-support/source-map-support.js:373:26
        Function.prepareStackTrace (node_modules/source-map-support/source-map-support.js:372:24)

  ✖ Test results were not received from test.js

[OmgImAlexis]

Assuming this is related then.

$ nyc ava 

  1 passed
  1 rejection

  Unhandled Rejection
  SyntaxError
    XMLHttpRequest.open (node_modules/jsdom/lib/jsdom/living/xmlhttprequest.js:486:15)
    dispatchXhrRequest (node_modules/axios/lib/adapters/xhr.js:45:13)
    xhrAdapter (node_modules/axios/lib/adapters/xhr.js:12:10)
    dispatchRequest (node_modules/axios/lib/core/dispatchRequest.js:52:10)

[sindresorhus]

@OmgImAlexis Not necessarily. Doesn't look like that error is coming from AVA or a dependent.

[OmgImAlexis]

Going off the warning from c01ac05 I had assumed it was related. If not feel free to remove my comments.

[pendar747]

I seem to get a similar error whenever I change fs.readFileSync!

   Uncaught Exception
  TypeError: Cannot read property 'sections' of undefined
    new SourceMapConsumer (node_modules/source-map/lib/source-map-consumer.js:20:19)
    mapSourcePosition (node_modules/source-map-support/source-map-support.js:175:14)
    wrapCallSite (node_modules/source-map-support/source-map-support.js:343:20)
    node_modules/source-map-support/source-map-support.js:378:26
    Function.prepareStackTrace (node_modules/source-map-support/source-map-support.js:377:24)

  × Test results were not received from dist\test\current\asset.spec.js

[mrozbarry]

I'm not 100% sure if this is related, but in ava 1.2.x with sinon 7.2.3, when I create a sandbox with mocked timers, I get an error that clearTimeout does not exist. I'm willing to open a new issue if this is unrelated, but it seems like it could be.

Ava 1.1.0 is not affected, so I think this has a specific issue with 1.2.0's clearTimeout methods. I'm not certain on the interaction with sinon's sandbox, though.

[novemberborn]

in ava 1.2.x with sinon 7.2.3, when I create a sandbox with mocked timers, I get an error that clearTimeout does not exist. I'm willing to open a new issue if this is unrelated, but it seems like it could be.

If you could open a new issue that'd be great. This issue is more about changing the fs module etc.

[novemberborn]

@mrozbarry this should be fixed with #2057.

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[novemberborn]

IMHO achieving this kind of isolation will have such an overhead as to not be worthwhile.