What is a TypeScript Parameterized Test?

A TypeScript parameterized test, also known as a data-driven test, is a testing technique where a single test function is executed multiple times with different sets of input values. Instead of writing separate test cases for each input scenario, you define a collection of inputs and expect a consistent behavior for each.

This approach offers several benefits:

- Reduced Code Duplication: Avoids repetitive code by running the same test logic with varying inputs.

- Enhanced Test Coverage: Easily test a wide range of scenarios, ensuring better coverage with minimal coding effort.

- Improved Readability: Keeps tests concise and easier to understand, as test logic isn't scattered across multiple test functions.

- Maintainability: When the logic of a test changes, you update it in one place instead of many.

How It Works:

Parameterized tests in TypeScript usually involve a testing framework (like Jest, Mocha, or others) that supports data-driven testing. You provide an array or collection of data sets. Each data set contains the inputs for one execution of the test function. The testing framework then runs the test for each data set.

Example using Jest:

Here's a simple example using Jest, a popular testing framework for JavaScript and TypeScript:

// Function to be tested
function add(a: number, b: number): number {
  return a + b;
}

// Test suite using parameterized tests with Jest
describe('add function', () => {
  test.each([
    [1, 2, 3],
    [0, 0, 0],
    [-1, 1, 0],
  ])('should return %i when adding %i and %i', (a, b, expected) => {
    expect(add(a, b)).toBe(expected);
  });
});

In this example:

- test.each() is used for parameterized tests in Jest.
- The array [[1, 2, 3], [0, 0, 0], [-1, 1, 0]] provides the inputs for each test execution.
- %i is used as a placeholder for each argument in the test case. - The test function will be run three times with different values from these data sets, checking that the result of the add function matches the expected result.

Key Advantages Revisited:

- Efficiency: Tests are easier to create and maintain for multiple scenarios.
- Clarity: A single, readable test function with varying inputs is easier to understand.
- Coverage: Parameterized tests facilitate better test coverage with less effort.

Using parameterized tests in TypeScript can significantly improve your testing practices by keeping your test suite concise, efficient, and comprehensive.

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