Writing Your First Test
test.js
To begin testing with Jest, you write a test using the test function. This function takes two arguments: a description string and a callback function containing the test logic. In the example above, the description string is 'adds 2 + 2 to equal 4'. This description should clearly state what you expect the test to do, making it easy to understand the purpose of the test when reading results or debugging.
Inside the callback function, you use the expect function. This function is essential for making assertions about your code. In this case, expect(2 + 2) creates an expectation for the value of 2 + 2. To check if this value matches what you expect, you use a matcher. Here, the matcher is toBe(4), which checks if the result of 2 + 2 is strictly equal to 4.
The combination of expect and toBe forms the core of many Jest tests. The expect function evaluates an expression, and the matcher, such as toBe, checks if the result meets your expectations. If the expectation passes, the test succeeds; if not, the test fails and Jest reports the error, helping you quickly identify issues in your code.
1. In a Jest test, what does the expect function do?
2. What is the purpose of the toBe matcher in Jest?
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test.js
To begin testing with Jest, you write a test using the test function. This function takes two arguments: a description string and a callback function containing the test logic. In the example above, the description string is 'adds 2 + 2 to equal 4'. This description should clearly state what you expect the test to do, making it easy to understand the purpose of the test when reading results or debugging.
Inside the callback function, you use the expect function. This function is essential for making assertions about your code. In this case, expect(2 + 2) creates an expectation for the value of 2 + 2. To check if this value matches what you expect, you use a matcher. Here, the matcher is toBe(4), which checks if the result of 2 + 2 is strictly equal to 4.
The combination of expect and toBe forms the core of many Jest tests. The expect function evaluates an expression, and the matcher, such as toBe, checks if the result meets your expectations. If the expectation passes, the test succeeds; if not, the test fails and Jest reports the error, helping you quickly identify issues in your code.
1. In a Jest test, what does the expect function do?
2. What is the purpose of the toBe matcher in Jest?
Thanks for your feedback!
