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You don't always have to type 'npm test' every time you want to check whether your changes pass or fail the tests. Mocha comes with a special '-- watch' flag that will automatically run any specified tests when it sees changes in a certain file or directory.
Video review
- You can write custom
mocha --watchcommands whenever you plan on working on one particular file a lot - You can also save a general
--watchcommand in yourpackage.jsonto run your tests all the time
For example:
"scripts": {
"test": "mocha",
"test:watch": "mocha --watch ./test ./"
}
The first argument describes the tests you want to run: all the tests in the ./test directory. The second argument describes the files you want to watch for changes: all the files in the current directory ./. You must include a . at the start of your file path, or Mocha will get confused on which files you’re looking for.
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If you're like me you might be
annoyed that you have to type npm test
0:00
every time you want to check whether
your changes pass or fail the test.
0:04
So Mocha comes with a special watch flag,
that will automatically run
0:08
any specified test when it sees changes
in a certain file or directory.
0:12
For example, when you launch the latest
workspace or open the project files for
0:17
this video.
0:21
You'll see that I filled in the spec we
started writing in the previous video for
0:22
the checkGameStatus function but I still
haven't finished the function itself.
0:27
So when I run checkGameStatus
on a player with one sunken ship
0:33
then the game should be over and
checkGameStatus should report false.
0:38
So, while I'm building this
function I want Mocha to
0:42
automatically run my tests every time
I make a change to checkGameStatus.
0:46
So that I'll know right away
when all my tests are passing.
0:51
We can do just that with the watch flag.
0:54
I've set up the initial function
in this new game instance,
0:57
that JS file,
located inside the game logic folder.
1:00
And running npm test in the console
shows that the test fails.
1:04
So it really breaks up our workflow
when we have to write code,
1:13
switch to the console, run npm test,
see the output and switch back.
1:17
We might make a lot of
changes to our functions and
1:21
it would be nice to know right away when
something works or something breaks.
1:24
So, to watch my gameinstance.js file,
I run mocha with the watch flag.
1:29
I need to tell mocha which test to run and
which file to watch.
1:35
So in this example if
I run mocha -- watch,
1:40
followed by the path to the game test
file, Then the path to the function file.
1:45
Mocha will run the suite found
in gametest.js every time
2:04
I save a change the file.
2:08
It runs right away and
I see the original failure.
2:10
So inside gameinstance.js if I set
2:12
the checkGameStatus function to
return false and save the file.
2:17
We see the console automatically
runs the test again, and
2:24
now they're passing, pretty cool.
2:27
So you can write custom moca --watch
commands like this whenever you plan to be
2:31
working on one particular file a lot.
2:35
But you can also save a general watch
command in your package.json file
2:38
to run your tests all
the time while you work.
2:42
That might be helpful for you to check
whenever you're unsure what's working and
2:45
what isn't working in the big picture,
while you build your application.
2:49
So, to set that up, let's go ahead and
open up the package.json file.
2:53
So in your script section,
after test, let's add a new command.
2:58
So first, we'll type test:watch,
the command we want here
3:04
should run all of our unit tests
whenever we make changes anywhere.
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So let's try mocha
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--watch ./test ./.
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Remember, the first argument
describes the tests we want to run,
3:27
all the tests in the test directory.
3:31
And the second argument describes
the files we want to watch for changes.
3:33
So, all the files in
the current directory.
3:37
And don't forget to add a period
at the start of your file path or
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mocha will get confused on
which files you're looking for.
3:44
All right so I'll go ahead and
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save my package.json file
then bring up the console.
3:50
And now, when I run npm run test:watch.
3:55
Mocha starts running all my tests, and
4:00
watches for
any file changes in my project.
4:04
So great I see all my
tests passed at first.
4:07
So now if for
example I open up the mainTest.js file and
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change an expectation to fail.
4:16
So let's say expect (true).to.be.false.
4:18
When I save the file we immediately see
the failing test results in the console.
4:23
And if I change it back to ok,
save the file,
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I see the passing test results again.
4:32
And if I open a game logic file,
like player_methods.js,
4:34
and comment out some important code.
4:39
Once I save the file I see
the tests are failing again.
4:44
So if I am uncomment the code, and
save, all my tests pass again.
4:50
Cool, so this is really useful.
4:55
And now to stop running watch you can
go over to the console and type Ctrl+C.
4:57
So if you have a lot of tests,
you might want to adapt this command so
5:07
that it doesn't run them all,
every time you make any change.
5:11
You can change a command to be more
specific to the part of the code you're
5:14
currently working with to save time and
improve performance.
5:18
And in your package.json file,
5:21
you can even set several different
commands like test:watch:playerMethods.
5:23
And set it to watch only
player_test.js and player_methods.js
5:29
that way it's easy to watch
different things at different times.
5:34
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