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Unit Testing/Jest/Test Exceptions

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Create a JavaScript Program

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Create the following JavaScript program. Save it as multiply.js

function multiply(x, y) {
    if (isNaN(x)) {
        throw new Error("x must be a number");
    }

    if (isNaN(y)) {
        throw new Error("y must be a number");
    }

    let result = x * y;
    return result;
}

module.exports = multiply;

Create a Test Program

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Create the following Jest test program. Save it as multiply.test.js

const multiply = require("./multiply");

test("Multiply 2 * 2", () => {
    expect(multiply(2, 2)).toBe(4);
});

test("Multiply 2 * x", () => {
    expect(() => {
        multiply(2, "x");
    }).toThrow("y must be a number");    
});

Test Success

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Test the program by running Jest in a terminal or command prompt in the same folder as the two programs above and observe the results.

npm test

Test Failure

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Change the multiply source code somehow, such as removing the number validation. Test the program by running Jest again and observe the results.