Mocha is a test framework to run tests.

https://mochajs.org/#assertions

Chai is an assertion library and you can find full documentation in the following link.

https://www.chaijs.com/api/bdd/

There are three type of assertion libraries in Chai.

• Expect
• Should
• Assert

expect and should use the same chainable language to construct assertions.

Assume that expect library is used like below

expect(firstName).to.be.a('string');
expect(firstName).to.equal('kenan');
expect(firstName).to.have.lengthOf(5);
expect(beverages).to.have.property('tea').with.lengthOf(3);

Above code could be written with should library like below.

firstName.should.be.a('string');
firstName.should.equal('kenan');
firstName.should.have.lengthOf(5);
beverages.should.have.property('tea').with.lengthOf(3);

You can find more detailed usage with Express, Mocha and Chai in the following repository

https://github.com/nodejs-projects-kenanhancer/express-demo.git

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