jest test each

Used for running a matrix of tests with expected outcomes.

Jest test.each documentation

Sample using positional arguments

For a function sum:

function sum(a, b) {
    return a + b;
}

A test matrix with it.each() would look like:

describe('sum', () => {
    test.each([
        [1, 1, 2],
        [1, 2, 3],
        [2, 1, 3],
    ])('sum of %i and %i should be %i', (a, b, expected) => {
        expect(a + b).toBe(expected);
    });
});

The test names generated would be:

• 'sum of 1 and 1 should be 2'
• 'sum of 1 and 2 should be 3'
• 'sum of 2 and 1 should be 3'

The generated names use Node printf, for positional arguments use:

• %p - pretty-format.
• %s- String.
• %d- Number.
• %i - Integer.
• %f - Floating point value.
• %j - JSON.
• %o - Object.
• %# - Index of the test case.
• %% - single percent sign ('%'). This does not consume an argument.

Named arguments

Or use objects and object destructuring for named arguments:

test.each([
    {a: 1, b: 1, expected: 2},
    {a: 1, b: 2, expected: 3},
    {a: 2, b: 1, expected: 3},
])('sum of $a and $b should be $expected', ({a, b, expected}) => {
    expect(a + b).toBe(expected);
});