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test-console

A simple and pragmatic library for testing Node.js console output.

Example

See the API section for more examples.

const stdout = require("test-console").stdout;

const output = stdout.inspectSync(() => {
    console.log("foo");
});
assert.deepEqual(output, [ "foo\n "]);

Installation

This is a Node.js library. Install Node, then:

npm install test-console (add --save or --save-dev if you want)

To use the library in your code, require it as follows:

const stdout = require("test-console").stdout;
const stderr = require("test-console").stderr;

API

  • stdout.inspect: Redirects writes to stdout into an array instead of writing them to console.
  • stdout.inspectSync: Just like inspect(), but automatically restores the console when done.
  • stdout.inspectAsync: Just like inspectSync(), but works with async functions.
  • stdout.ignore: Prevent writes to stdout from appearing on the console.
  • stdout.ignoreSync: Just like ignore(), but automatically restores the console when done.
  • stdout.ignoreAsync: Just like ignoreSync(), but works with async functions.

All functions accept an optional options object as the first argument, where isTTY is the only available option. isTTY, if defined, will override the stdout field of the same name.

The same API is also available on stderr.

inspect = stdout.inspect(options)

Redirects writes to stdout into an array instead of writing them to the console.

  • options: object [optional]

    • isTTY: If not undefined, this value will be used to temporarily overwrite stdout.isTTY.
  • inspect: Returned as an EventEmitter with two properties and one event:

    • inspect.output: An array containing one string for each call to stdout.write(). This array updates every time another call to stdout.write() is made.
    • inspect.restore(): Call this function to restore stdout.write() to its normal behavior.
    • data event: This event fires every time stdout.write() is called.

Example of using inspect() to test a synchronous function:

const inspect = stdout.inspect();
functionUnderTest();
inspect.restore();
assert.deepEqual(inspect.output, [ "foo\n" ]);

Example of using inspect() to test an asynchronous function with await:

const inspect = stdout.inspect();
await functionUnderTestAsync();
inspect.restore();
assert.deepEqual(inspect.output, [ "foo\n" ]);

Example of using inspect() to test an asynchronous function with a callback:

const inspect = stdout.inspect();
functionUnderTest(() => {
    inspect.restore();
    assert.deepEqual(inspect.output, [ "foo\n" ]);
});

Example of using inspect() to listen for an event:

const inspect = stdout.inspect();
let output = "";
inspect.on("data", (chunk) => {
    output += chunk;
});
functionUnderTestAsync();
inspect.restore();
assert.equal(output, "foo\n");

output = stdout.inspectSync(options, fn)

output = stdout.inspectSync(fn)

Just like inspect(), but automatically restores the console when done.

  • options: object [optional]

    • isTTY: If not undefined, this value will be used to temporarily overwrite stdout.isTTY.
  • fn(output): The function to run while inspecting stdout. After the function returns, stdout.write is automatically restored. Note that output is passed into this function in addition to being returned from inspectSync().

  • output: Passed into fn and also returned as an array. Contains one string for each call to stdout.write(). This array updates every time another call to stdout.write() is made.

Example of using inspectSync() to test a synchronous function:

const output = stdout.inspectSync(() => {
    functionUnderTest();
});
assert.deepEqual(output, [ "foo\n" ]);

Example of using `inspectSync() to incrementally test several synchronous functions:

stdout.inspectSync((output) => {
    functionUnderTest();
    assert.deepEqual(output, [ "foo\n" ]);
    anotherFunctionUnderTest();
    assert.deepEqual(output, [ "foo\n", "bar\n" ]);
});

output = await stdout.inspectAsync(options, fn)

output = await stdout.inspectAsync(fn)

Just like inspectSync(), but works with asynchronous functions.

  • options: object [optional]

    • isTTY: If not undefined, this value will be used to temporarily overwrite stdout.isTTY.
  • fnAsync(output): The function to run while inspecting stdout. After the function returns, stdout.write is automatically restored. Note that output is passed into this function in addition to being returned from inspectSync().

  • output: Passed into fnAsync and also returned as an array containing one string for each call to stdout.write(). This array updates every time another call to stdout.write() is made.

Example of using inspectAsync() to test an asynchronous function:

const output = await stdout.inspectAsync(async () => {
    await functionUnderTestAsync();
});
assert.deepEqual(output, [ "foo\n" ]);

Example of using `inspectAsync() to incrementally test several asynchronous functions:

await stdout.inspectAsync(async (output) => {
    await functionUnderTestAsync();
    assert.deepEqual(output, [ "foo\n" ]);
    await anotherFunctionUnderTestAsync();
    assert.deepEqual(output, [ "foo\n", "bar\n" ]);
});

restore = stdout.ignore(options)

Prevent writes to stdout from appearing on the console.

  • options: object [optional]

    • isTTY: If not undefined, this value will be used to temporarily overwrite stdout.isTTY
  • restore(): Call this function to restore stdout.write to its normal behavior.

Example of using ignore() to prevent a synchronous function from writing to the console:

const restore = stdout.ignore();
functionUnderTest();
restore();

Example of using ignore() to prevent an asynchronous function with a callback from writing to the console:

const restore = stdout.ignore();
functionUnderTest(() => {
    restore();
});

Example of using ignore() to prevent a suite of tests from writing to the console:

let restoreStdout;

beforeEach(() => {
    restoreStdout = stdout.ignore();
});

afterEach(() => {
    restoreStdout();
});

// tests go here

ignoreSync(options, fn)

ignoreSync(fn)

Just like ignore(), but automatically restores the console when done.

  • options: object [optional]

    • isTTY: If not undefined, this value will be used to temporarily overwrite stdout.isTTY
  • fn(): The function to run while ignoring stdout. After the function returns, stdout.write is automatically restored.

Example of using ignoreSync() to prevent a synchronous function from writing to the console:

stdout.ignoreSync(() => {
    functionUnderTest();
});

await ignoreAsync(options, fnAsync)

await ignoreAsync(fn)

Just like ignoreSync(), but works with async/await.

  • options: object [optional]

    • isTTY: If not undefined, this value will be used to temporarily overwrite stdout.isTTY
  • fnAsync(): The function to run while ignoring stdout. After the function returns, stdout.write is automatically restored.

Example of using ignoreSync() to prevent an asynchronous function from writing to the console:

await stdout.ignoreAsync(async () => {
    await functionUnderTestAsync();
});

Version History

2.0.0: Add events to inspect(). Add inspectAsync(), ignoreAsync(). BREAKING CHANGE: Requires Node 7.6.0 or higher (due to async/await support)

1.1.0: Add ability to override stdout.isTTY (and stderr.isTTY).

1.0.0: API fails with nice error messages when called with wrong number of arguments.

0.7.1: Bug fix: Sync() versions restore old behavior even if exception occurs

0.7.0: Initial release: inspect(), inspectSync(), ignore(), and ignoreSync()

Contributors

Created by James Shore. Inspired by Brandon Satrom's Automated Testing of Standard Output in Node.js.

Option for mocking isTTY added by Jason Boileau.

Inspect data event added by Tim Toohey.

Release Process

  1. Update version history in readme
  2. Ensure clean build: ./jake.sh
  3. Update npm version: npm version [major|minor|patch]
  4. Release to npm: npm publish
  5. Release to github: git push && git push --tags

License

The MIT License (MIT)

Copyright (c) 2014-2015 James Shore

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.