@MethodSource is a repeatable ArgumentsSource which provides access to values returned from factory methods of the class in which this annotation is declared or from static factory methods in external classes referenced by fully qualified method name.

Each factory method must generate a stream of arguments, and each set of "arguments" within the "stream" will be provided as the physical arguments for individual invocations of the annotated org.junit.jupiter.params.ParameterizedClass @ParameterizedClass or @ParameterizedTest. Generally speaking this translates to a Stream of Arguments (i.e., Stream<Arguments>); however, the actual concrete return type can take on many forms. In this context, a "stream" is anything that JUnit can reliably convert into a Stream, such as Stream, DoubleStream, LongStream, IntStream, Collection, Iterator, an array of objects or primitives, or any type that provides an Iterator-returning iterator() method (such as, for example, a kotlin.sequences.Sequence). Each set of "arguments" within the "stream" can be supplied as an instance of Arguments, an array of objects (e.g., Object[], String[], etc.), or a single value if the parameterized test method accepts a single argument.

If the return type is Stream or one of the primitive streams, JUnit will properly close it by calling BaseStream.close(), making it safe to use a resource such as Files.lines().

Please note that a one-dimensional array of objects supplied as a set of "arguments" will be handled differently than other types of arguments. Specifically, all of the elements of a one-dimensional array of objects will be passed as individual physical arguments to the @ParameterizedTest method. This behavior can be seen in the table below for the static Stream<Object[]> factory() method: the @ParameterizedTest method accepts individual String and int arguments rather than a single Object[] array. In contrast, any multidimensional array supplied as a set of "arguments" will be passed as a single physical argument to the @ParameterizedTest method without modification. This behavior can be seen in the table below for the static Stream<int[][]> factory() and static Stream<Object[][]> factory() methods: the @ParameterizedTest methods for those factories accept individual int[][] and Object[][] arguments, respectively.

Examples

The following table displays compatible method signatures for parameterized test methods and their corresponding factory methods.

Compatible method signatures and factory methods

@ParameterizedTest method	Factory method
void test(int)	static int[] factory()
void test(int)	static IntStream factory()
void test(String)	static String[] factory()
void test(String)	static List<String> factory()
void test(String)	static Stream<String> factory()
void test(String, String)	static String[][] factory()
void test(String, int)	static Object[][] factory()
void test(String, int)	static Stream<Object[]> factory()
void test(String, int)	static Stream<Arguments> factory()
void test(int[])	static int[][] factory()
void test(int[])	static Stream<int[]> factory()
void test(int[][])	static Stream<int[][]> factory()
void test(Object[][])	static Stream<Object[][]> factory()

Factory methods within the test class must be static unless the PER_CLASS test instance lifecycle mode is used; whereas, factory methods in external classes must always be static.

This behavior and the above examples also apply to parameters of a @ParameterizedClass, regardless whether field or constructor injection is used.

Factory methods can declare parameters, which will be provided by registered implementations of org.junit.jupiter.api.extension.ParameterResolver.

Inheritance

This annotation is inherited to subclasses.