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Testing with JavaScript Lab

Learning Goals

  • Running tests
  • Reading test results

Running Tests

You understand how to read tests; now it's time to run the tests.

Recall that in the previous lesson, the tests were commented out. Be sure to fork and clone this lab into your local environment so you have the version of the test file that is not commented out. (Return to the previous lesson if you need a reminder of how to do this.)

Navigate into its directory in the terminal, then run code . to open the files in Visual Studio Code. (If you are using a different text editor, the command will be different.) Finally, run npm install to install the lab's dependencies.

What exactly do we mean by installing dependencies? Open the package.json file and scroll down to the bottom. You'll see a list of 'DevDependencies'. What's listed here are JavaScript packages: files or sets of files full of existing, reusable code. They are designed to be shared, allowing many developers to use the same code in their own projects. The packages you see listed in package.json make it possible to run the lab's tests. In order to use the packages, we have to install them; npm install does that for us.

If you take a look at index.js and indexTest.js, you should see the same code as in the previous lesson. The only difference is that the test code in indexTest.js is no longer commented out.

Important: You should never need to make changes to test files unless a lab's instructions specifically tell you to do so.

To run the tests, run npm test in the terminal. That's it!

The next step is learning how to read the results that the tests give you.

Reading Results of Tests

The first time you run npm test, you should see something that looks like this:

> [email protected] test
> mocha --timeout 5000 -R mocha-multi --reporter-options spec=-,json=.results.json


  what-is-a-test
    Name
      1) returns "Susan"
    Height
      2) is less than 40 and greater than 0
    Message
      ✓ gives the name and height


  1 passing (552ms)
  2 failing

  1) what-is-a-test
       Name
         returns "Susan":

      Error: Expected 'Joe' to equal 'Susan'
      + expected - actual

      -Joe
      +Susan

      at assert (node_modules/expect/lib/assert.js:29:9)
      at Expectation.toEqual (node_modules/expect/lib/Expectation.js:81:30)
      at Context.<anonymous> (test/indexTest.js:6:26)
      at processImmediate (internal/timers.js:461:21)

  2) what-is-a-test
       Height
         is less than 40 and greater than 0:
     Error: Expected 74 to be less than 40
      at assert (node_modules/expect/lib/assert.js:29:9)
      at Expectation.toBeLessThan (node_modules/expect/lib/Expectation.js:156:28)
      at Context.<anonymous> (test/indexTest.js:13:28)
      at processImmediate (internal/timers.js:461:21)

npm ERR! Test failed.  See above for more details.

Note: If you also get an error that ends with "unexpected character (after ) at line 1, column 1 [parse.c:769] (Oj::ParseError)", make sure you've cloned down the files for this lab, and are not running the tests on the files from the previous lesson.

Let's break this down a bit. If you look about a third of the way down in the output, you'll see a summary of how the tests went:

  1 passing (552ms)
  2 failing

Great! We've already got one test passing! Now let's see how we failed the other two tests.

  1) what-is-a-test
       Name
         returns "Susan":

      Error: Expected 'Joe' to equal 'Susan'
      + expected - actual

      -Joe
      +Susan

      at assert (node_modules/expect/lib/assert.js:29:9)
      at Expectation.toEqual (node_modules/expect/lib/Expectation.js:81:30)
      at Context.<anonymous> (test/indexTest.js:6:26)
      at processImmediate (internal/timers.js:461:21)

  2) what-is-a-test
       Height
         is less than 40 and greater than 0:
     Error: Expected 74 to be less than 40
      at assert (node_modules/expect/lib/assert.js:29:9)
      at Expectation.toBeLessThan (node_modules/expect/lib/Expectation.js:156:28)
      at Context.<anonymous> (test/indexTest.js:13:28)
      at processImmediate (internal/timers.js:461:21)

While there is no hard and fast rule, and there will be exceptions, it is most often best to address your test errors in order. So let's take a look at our first error:

1) what-is-a-test
       Name
         returns "Susan":

      Error: Expected 'Joe' to equal 'Susan'
      + expected - actual

      -Joe
      +Susan

      at assert (node_modules/expect/lib/assert.js:29:9)
      at Expectation.toEqual (node_modules/expect/lib/Expectation.js:81:30)
      at Context.<anonymous> (test/indexTest.js:6:26)
      at processImmediate (internal/timers.js:456:21)

Here is the specific error:

      Error: Expected 'Joe' to equal 'Susan'
      + expected - actual

      -Joe
      +Susan

It tells us what the test is expecting (Expected 'Joe' to equal 'Susan') and then gives us details about the expected and actual values. This shows you exactly how the value your code is returning (the actual value) differs from what the test is looking for. Make sure you understand what this is telling you — it will come in handy in later labs!

This error makes sense because we have the name variable set equal to "Joe" in our index.js file. Let's change that line of code to set name equal to "Susan" instead. Run the tests again by typing npm test in the terminal's command line (don't forget to save the file first!), and you should see that we are now passing 2 of the 3 tests!

  what-is-a-test
    Name
      ✓ returns "Susan"
    Height
      1) is less than 40 and greater than 0
    Message
      ✓ gives the name and height


  2 passing (736ms)
  1 failing

  1) what-is-a-test
       Height
         is less than 40 and greater than 0:
     Error: Expected 74 to be less than 40
      at assert (node_modules/expect/lib/assert.js:29:9)
      at Expectation.toBeLessThan (node_modules/expect/lib/Expectation.js:156:28)
      at Context.<anonymous> (test/indexTest.js:13:28)
      at processImmediate (internal/timers.js:461:21)

Woot! You passed another one. Now go ahead and try to pass the remaining test on your own.

Common Errors

While you are solving the other tests you may come across a few errors. Let's go over some common ones:

Variable Not Defined

ReferenceError: name is not defined

That one says that the name variable is not defined. That makes no sense! We initialized the name variable in index.js! What that actually means is that the test couldn't find the variable name. You'll get this error if the name of one of your variables is different than the test is expecting. Check to make sure you used the correct variable names and look carefully for typos.

Unexpected Identifier

/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/index.js:1
cnst name = "Susan";
     ^^^^

SyntaxError: Unexpected identifier
    at wrapSafe (internal/modules/cjs/loader.js:979:16)
    at Module._compile (internal/modules/cjs/loader.js:1027:27)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at Object.<anonymous> (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/test/indexTest.js:1:15)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at /Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/lib/mocha.js:311:36
    at Array.forEach (<anonymous>)
    at Mocha.loadFiles (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/lib/mocha.js:308:14)
    at Mocha.run (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/lib/mocha.js:849:10)
    at Object.exports.singleRun (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/lib/cli/run-helpers.js:108:16)
    at exports.runMocha (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/lib/cli/run-helpers.js:143:13)
    at Object.exports.handler (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/lib/cli/run.js:305:3)
    at Object.runCommand (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/yargs/lib/command.js:242:26)
    at Object.parseArgs [as _parseArgs] (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/yargs/yargs.js:1104:24)
    at Object.parse (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/yargs/yargs.js:566:25)
    at Object.exports.main (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/lib/cli/cli.js:68:6)
    at Object.<anonymous> (/Users/lizburton_fs/Development/code/phase-0-pac-3-what-is-a-test-lab/node_modules/mocha/bin/mocha:133:29)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47
npm ERR! Test failed.  See above for more details.

Whoa! So many words that make no sense. Don't worry though. The most important line is the SyntaxError: Unexpected identifier line. What that means is you have some sort of typo or syntax mistake. It could be a HUGE variety of things but usually, JS will try and give you a hint. This time it's pointing to the cnst name = "Susan" line of code. Take a look and read very carefully: const is misspelled. Whoops! Once we fix that everything will work.

One note on this type of error is that it is sort of a catch-all. Tons and tons of problems end in that sort of error message. Whenever you see it, be sure to read over your code with a fine-toothed comb... and you'll find the problem!

Type Errors

On the second test, there is a chance you might see the following error:

1) what-is-a-test
       Height
         is less than 40 and greater than 0:
     Error: The "actual" argument in expect(actual).toBeLessThan() must be a number
      at assert (node_modules/expect/lib/assert.js:29:9)
      at Expectation.toBeLessThan (node_modules/expect/lib/Expectation.js:156:28)
      at Context.<anonymous> (test/indexTest.js:13:28)
      at processImmediate (internal/timers.js:456:21)

This error is slightly different than the last two. In this case, the test is giving us a unique message because it recognizes a problem. If we look at this test in test/indexTest.js, we see this:

describe("Height", () => {
    it("is less than 40 and greater than 0", () => {
      expect(height).toBeMoreThan(0)
      expect(height).toBeLessThan(40);
    });
  });

We can see that the word "actual" in this case is referring to the height variable. The error message is telling us that height must be a number. If you're seeing this, make sure that you have set the height variable to a number that's less than 40 (e.g. 39), not a string ("39"). The test will interpret the value as a string due to the quotation marks wrapping it.

Optional Mocha Configuration

In this lab, we only had three tests to pass, but as you continue through the curriculum you will encounter labs with many more tests. You can imagine that the test output could get very long, making it more difficult to focus in on how to fix a particular error.

To help with this issue, there is some very simple setup you can put in place in Mocha that will cause the tests to stop as soon as the first failing test is encountered.

To implement this, open up the package.json file and find the test script. It should look something like this:

"test": "mocha --timeout 5000 -R mocha-multi --reporter-options spec=-,json=.results.json"

Add the --bail flag to the end of the line, inside the quotes:

"test": "mocha --timeout 5000 -R mocha-multi --reporter-options spec=-,json=.results.json --bail"

That's it!

Submitting Your Work to Canvas

Once you've got all the tests passing, it's time to push your completed code up to GitHub and submit it to Canvas using CodeGrade. We'll do a quick review of how to do that below, but you may want to review the full process in the Complete Your First Software Engineering Assignment lesson. You'll be going through this process for every lab you do in this program!

Let's review the process. First, you need to "stage" your changes using the git add command:

$ git add index.js

or

$ git add .

Recall that the . shortcut will stage all files that have changes. In this case there's only one so either command will work.

Next, you need to "commit" your changes, which basically saves a record of the changes you've made. Don't forget to use the -m flag and include a commit message! Use the message shown below or choose your own:

$ git commit -m "complete lab"

Finally, push your changes up to your GitHub account (your fork of this lab):

$ git push

If you go back to your repo in GitHub and refresh the page, you should now see a new commit with your commit message.

The final step is to submit your work to Canvas:

  1. Scroll to the bottom of this lesson page in Canvas and click the button labeled "Load Review: Variables Lab in a new window".
  2. In the CodeGrade window that opens, click "Create Submission". You should now see a list of your repositories.
  3. Find the repo for this lab and click Connect.
  4. When you get the message that your repo has been connected, click on the embedded link, then the "AutoTest" tab to watch your progress. Once the tests have finished running, you should see the green checkmark in the "Pass" column, indicating that you've successfully completed the lab.

CodeGrade window showing tests have all been passed

Note about the git push command

You may recall from the Complete Your First Software Engineering Assignment lesson that a different form of the git push command was used:

$ git push <remote> <branch>

where remote is the "alias" for the repo's url on GitHub, and branch is the repo's default branch (generally main for newer repos and master for older ones). For this lab, therefore, the full command would be:

$ git push origin master

This command tells git to push the code in the master branch of the local repo to the master branch of the remote repo identified by the origin alias.

So why didn't you need to run that command?

When you use the git clone command to clone down a repo from GitHub, git automatically assigns the "origin" alias to the url you clone from, and uses the default branch for that repo.

As you work through the labs in this program, you should always:

  1. fork the lab's repo to your GitHub account, and
  2. clone that fork down to your local machine.

As long as you always fork before you clone, it should be safe to run git push without specifying the remote and branch.

If you want to verify that you're pushing to the right repo, you can use the git remote command and include the -v flag:

$ git remote -v
origin	[email protected]:your-github-username/phase-0-pac-3-what-is-a-test-lab.git (fetch)
origin	[email protected]:your-github-username/phase-0-pac-3-what-is-a-test-lab.git (push)

Here you can see that the origin alias points to your fork of the repo, so it's safe to run the shorter command, git push.

Conclusion

Now that you've gotten all your tests passing and submitted your work (and learned a bit more about git push), you're ready to move on. Congratulations! You've solved your first JavaScript tests!