Chai is an assertion library. Instead of needing to write several variations of
assert, Chai provides several different methods that we can use to create tests that are easy to read. Chai also uses method chaining to create a more English-like version of the test, so they are both easy to read and write.
For more information on Chai, visit http://www.chaijs.com.
Chai is useful because it allows us to write expressive tests without a lot of work. It also caters to you, the developer, by letting you choose one of several provided interfaces. There are three:
assert: Tests use an assert-styled interface, akin to what we used in the prior section. There are a lot of utility methods that you can use, such as