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Automate and Organize Tests

Teardown

Some tests require a fourth phase called teardown. This step makes your test isolated.

Teardown - reset any conditions that were changed during the test

A test, like the example in this exercise, can make changes to its environment that could affect other tests. The teardown phase is used to reset the environment before the next test runs.

Some common changes to an environment include

altering files and directory structure
changing read and write permissions on a file
editing records in a database

In some cases — including the previous exercise — the teardown phase isn’t needed because there are no conditions to reset.

Instructions

This exercise uses Node’s filesystem library fs in addition to assert. It’s okay if you’re not familiar with fs: each function is described in comments.

The call to fs.appendFileSync(path, str) will do one of two things:

If a file at path does not exist, the method creates the file and adds the string str to that file.
If the file does exist, the method adds the string str to the end of the file.

The current test does not have a teardown phase. Run it using the terminal.

Run the test suite again. Compare this output to the output of the previous test run.

Note the new file message.txt created in your directory.

project
|_ node_modules
|_ test
|___ index_test.js
|_ message.txt
|_ package.json

You got different output because the test was not isolated.

In the first run the file didn’t exist, so fs.appendFileSync created a message.txt file containing the string.
In the second run, the method added the string to the end of message.txt because it already existed.

In the terminal enter rm message.txt to delete the file.

Add this code below // Teardown. This method will delete the file at path before the test finishes.

fs.unlinkSync(path);

Verify that you fixed the issue: run the test suite twice and compare the outputs.

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