What are the best practices for unit testing PHP functions?

Best practices for unit testing functions include using assertion libraries to simplify test writing and provide methods for direct comparison and verification. Write tests for each function covering various input scenarios, including boundary conditions and error conditions. Use independent data to ensure tests are independent of other logic by mocking dependencies. Avoid duplicating code and use setup methods or helper functions to improve maintainability. Keep tests simple, incorporate complex logic into helper functions, and maintain a single responsibility.

PHP Function Unit Testing Best Practices

Unit testing is critical to ensuring the correctness of functions in your code base. Here are some best practices that can help you write high-quality unit tests:

1. Use an assertion library

Use something like PHPUnit Assertion libraries make it possible to write clear and understandable tests. The assertion library provides methods such as assertEquals(), assertTrue(), etc., allowing you to compare and verify directly.

2. Write tests for each function

Write at least one test for each function to ensure it operates as expected. Tests should cover a variety of input scenarios, including boundary conditions and error conditions.

3. Use independent data

Ensure that the test has nothing to do with other tests and function logic. Use independent data to achieve this by simulating dependencies. For example, you can use a mock object to simulate a database connection.

4. Avoid duplicating code

Use setters or helper functions to avoid setting or getting data repeatedly in multiple tests. This will make your code easier to maintain.

5. Keep tests simple

Tests should be as short and concise as possible. Put complex logic into helper functions and keep tests on a single responsibility.

Practical case:

Suppose we have a calculateDiscount() function that calculates the discount amount based on the total amount of the order and the discount code. We can test this function with the following test:

use PHPUnit\Framework\TestCase;

class DiscountCalculatorTest extends TestCase
{
    public function testCalculateDiscount()
    {
        $calculator = new DiscountCalculator();
        $discount = $calculator->calculateDiscount(100, 'LOYALTY');
        $this->assertEquals(10, $discount);
    }

    public function testInvalidDiscountCode()
    {
        $calculator = new DiscountCalculator();
        $this->expectException(InvalidArgumentException::class);
        $calculator->calculateDiscount(100, 'INVALID');
    }
}

This test verifies that the function calculates the discount correctly and throws an exception when an invalid discount code is provided.

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