assert

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We already learned how to organize and automate tests using the Mocha test framework. To write the test themselves, we can use the assert.ok method provided by Node.js. In programming, a test compares an expected outcome to an actual outcome. For example, we expect the outcome of the following code to be : a has a value of 3.

const a = 1 + 2;

To test the value saved to a with plain JavaScript, you would need to write a conditional statement comparing a to the expected result. Inside the statement, you would construct an error when the actual outcome does not match the expected.

if (a !== 3) {
throw 'Test failed! a is not a 3'
}

assert.ok() allows you to compare values and throw errors as needed using one function call. The small, human-readable format of the functions will help you make a more expressive test suite. As a Node module, assert can be imported at the top of your files with:

const assert = require('assert');

assert.ok(a === 3):

In this case a === 3 evaluates to true, so no error is thrown.
If an argument passed to assert.ok() evaluates to false, an AssertionError in thrown. The error communicates to Mocha that a test has failed, and Mocha logs the error message to the console.

[oldoc63]

1. At the top of index_test.js, import assert with the require function.
2. Within the provided it block, enter the following and expression.