Creating a custom matcher

In Chapter 2, Testing Concepts, we read that unit tests act as documentation to the project. In order for them to be descriptive, success and failure messages of tests should be very clear. But, sometimes, the default matchers as explained previously, are not sufficient or leave us with unexpected, unclear messages when fail or pass. For example, our expectation is:

expect(employee.salary).toEqual(9000);

This results in failure because the actual salary was 4,000.

Expected 1000 to equal 9000.

By looking at the message, you cannot detect what the context was. How about if it was something like: "Expected salary of employee was 9000 but found to be 4000". This message gives us an idea from the message itself that the salary ...

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