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Imagine you need to test a function with many different inputs. Writing a separate test for each input can be tedious and repetitive.

Data-driven testing allows you to run the same test logic multiple times, but with different sets of data for each run. This makes your tests more efficient and easier to maintain.

Parameterized tests in JUnit 5 let you write a single test method that can be executed multiple times with different arguments. Instead of copying and pasting test code, you supply the data, and JUnit handles the iterations.

• Saves time and reduces boilerplate code.
• Improves test coverage by easily testing edge cases.
• Makes tests more readable and maintainable.

To create a parameterized test, you use the @ParameterizedTest annotation instead of @Test. You also need to provide a source for the arguments.

JUnit 5 offers several argument sources, like @ValueSource for single arguments or @CsvSource for multiple arguments. Let's look at @ValueSource first.

The @ValueSource annotation is perfect for providing simple, primitive data types directly in your test. It supports strings, ints, longs, doubles, and more.

Each value in the source will cause the test method to run once with that value as an argument.

Here's a simple example testing if strings are not null or empty. Notice how the test method accepts a String parameter.

When your test method needs more than one argument, @CsvSource comes in handy. It lets you define arguments as comma-separated values (CSV).

Each string in the @CsvSource array represents a row of data, and values are split by commas to match the test method's parameters.

Let's test a simple addition function. Each line in @CsvSource provides two numbers and their expected sum.

Sometimes, the test data or even the number of tests isn't known until runtime. This is where Dynamic Tests shine!

Instead of defining all tests at compile time, dynamic tests allow you to generate them programmatically during test execution. This is useful for complex scenarios or external data sources.

To create dynamic tests, you use the @TestFactory annotation. A method annotated with @TestFactory doesn't run a test itself, but rather produces a collection of DynamicTest instances.

• @TestFactory methods must return a Stream, Collection, Iterable, or Iterator of DynamicTest.
• Each DynamicTest instance has a display name and an executable lambda.

Here's an example generating tests for string lengths. Each test is created on the fly based on a list of words.

Great job! You've learned how to make your JUnit tests more flexible and efficient:

• Parameterized Tests (@ParameterizedTest with sources like @ValueSource, @CsvSource) allow you to run the same test logic with multiple, predefined data sets.
• Dynamic Tests (@TestFactory) let you generate tests programmatically at runtime, ideal for scenarios where test cases are discovered dynamically.

These features help you write cleaner, more comprehensive tests with less effort!