How to assert the output of process.stderr?
2 answers
Install Mocha if you haven't:
npm install -g mocha
shouldpass.js:
process.stderr.write('omg')
shouldfail.js:
process.stdout.write('not omg on stderr')
test.js:
var exec = require('child_process').exec
, assert = require('assert')
describe('run tests', function(){
it('should pass', function(done) {
exec('node ./shouldpass.js', function(err, stdout, stderr) {
assert.equal(stderr, 'omg')
done()
})
})
it('should fail', function(done) {
exec('node ./shouldfail.js', function(err, stdout, stderr) {
assert.equal(stderr, 'omg')
done()
})
})
})
For start:
mocha test.js
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You can temporarily overwrite process.stdout.write
, buffer the input and use console.error
to print the output ( console.log
won't work if process.stdout.write
overwritten), for example
describe('process.stdout', () => {
let processStdoutWrite,
processStdoutWriteBuffer,
overwriteProcessStdoutWrite,
resetProcessStdoudWrite,
getProcessStdoutBuffer;
/**
* @var {function} Reference to the original process.stdout.write function.
*/
processStdoutWrite = process.stdout.write;
/**
* @returns {undefined}
*/
overwriteProcessStdoutWrite = () => {
processStdoutWriteBuffer = '';
process.stdout.write = (text) => {
processStdoutWriteBuffer += text;
};
};
/**
* @returns {string}
*/
getProcessStdoutBuffer = () => {
return processStdoutWriteBuffer;
};
/**
* @returns {undefined}
*/
resetProcessStdoudWrite = () => {
process.stdout.write = processStdoutWrite;
};
beforeEach(() => {
overwriteProcessStdoutWrite();
});
afterEach(() => {
resetProcessStdoudWrite();
});
describe('.write()', () => {
it('prints "foo"', () => {
process.stdout.write('foo');
process.stdout.write('bar');
console.error(getProcessStdoutBuffer());
});
});
});
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