Add List-based support to Arguments API #4574

mariokhoury4 · 2025-05-24T22:39:31Z

Overview

This PR adds List-based support to the Arguments API for parameterized tests.

New additions:

Arguments.of(List<@Nullable Object>)
Arguments.arguments(List<@Nullable Object>) (alias)
Arguments.argumentSet(String, List<@Nullable Object>)
Arguments.toList() — returns a mutable List<@Nullable Object>

These additions make it easier to dynamically build arguments from collections when using @ParameterizedTest.

All additions are tested in ArgumentsTests.java.

Fixes #4535

I hereby agree to the terms of the JUnit Contributor License Agreement.

Definition of Done

There are no TODOs left in the code
Method preconditions are checked and documented in the method's Javadoc
Coding conventions (e.g. for logging) have been followed
Change is covered by automated tests including corner cases, errors, and exception handling
Public API has Javadoc and @API annotations
Change is documented in the User Guide and Release Notes

…toList)

marcphilipp · 2025-05-25T11:21:51Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	static Arguments of(@Nullable List<@Nullable Object> arguments) {
+		if (arguments == null) {
+			return of((Object) null); // Properly wrap null
+		}


Suggested change

static Arguments of(@Nullable List<@Nullable Object> arguments) {

if (arguments == null) {

return of((Object) null); // Properly wrap null

}

static Arguments of(List<@Nullable Object> arguments) {

Preconditions.notNull(arguments, "arguments must not be null");

marcphilipp · 2025-05-25T11:22:51Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+		if (arguments.isEmpty()) {
+			// Must still return empty arguments array
+			return of(new Object[0]);
+		}
+		return () -> arguments.toArray(new Object[0]);


Suggested change

if (arguments.isEmpty()) {

// Must still return empty arguments array

return of(new Object[0]);

}

return () -> arguments.toArray(new Object[0]);

return of(arguments.toArray());

marcphilipp · 2025-05-25T11:23:21Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	static ArgumentSet argumentSet(String name, List<@Nullable Object> arguments) {
+		Preconditions.notBlank(name, "name must not be null or blank");
+		Preconditions.notNull(arguments, "arguments list must not be null");
+		return new ArgumentSet(name, arguments.toArray(new Object[0]));


Suggested change

return new ArgumentSet(name, arguments.toArray(new Object[0]));

return new ArgumentSet(name, arguments.toArray());

marcphilipp · 2025-05-25T11:26:43Z

...t-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EmptyArgumentsProvider.java

-			return Stream.of(arguments(Collections.emptyList()));
+			return Stream.of(Arguments.of((Object) Collections.emptyList()));


This makes me wonder whether we should choose different names instead of overloading of(), arguments(), and argumentSet() to avoid such breakages. Maybe copyOf, argumentsOf, and argumentSetOf()?

@junit-team/junit-5 WDYT?

Well, we unfortunately overlooked the fact that a single List is also a single Object, so we definitely cannot go with this as-is.

Existing code must still compile without adding casts.

Though, in our defense, it is easy to overlook something like that when "coding in the browser". 😉

Maybe copyOf, argumentsOf, and argumentSetOf()?

I would rather go with something consistent, instead of having "copy" in only one of the names.

How about something like fromList(), argumentsFromList(), and argumentSetFromList()?

We could also drop the List part of the names, if we are somehow sure we will never introduce yet-another-set-of-overloads. So, something like from(), argumentsFrom(), and argumentSetFrom().

Thoughts?

Thanks for the thoughtful feedback! I agree that it's important to avoid breaking existing usage. I also like the idea of going with a more general naming convention, so my preference would be to use from() instead of fromList() or argumentsFrom(). I'm happy to update the PR accordingly once there's consensus.

+1 on the shorter variants. We might even get away with adding overloads to that in the future because "conflicts" with List seem less likely than with Object...

I have updated the code with the suggestions!

I'd pondered it more while away from the computer and decided that I'm in favor of the from(), argumentsFrom() and argumentSetFrom() variants because of the brevity and also because of the nice symmetry with the new toList() instance method.

from(List) and toList() work well together.

So, I'm glad to see you both agree and that you're already implemented the changes, @mariokhoury4. 👍

marcphilipp · 2025-05-25T11:27:18Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

@@ -172,4 +176,72 @@ public String toString() {

 	}

+	/**


Please move these next to the other static factory methods above.

Thanks for the suggestion! I'll move the method next to the other static factory methods to keep things consistent.

…est accordingly

marcphilipp · 2025-05-26T06:36:24Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

@@ -125,6 +129,77 @@ static ArgumentSet argumentSet(String name, @Nullable Object... arguments) {
 		return new ArgumentSet(name, arguments);
 	}

+	/**
+	 * Factory method for creating an instance of {@code Arguments} based on
+	 * the supplied {@code arguments} as a {@link List}.


Suggested change

* the supplied {@code arguments} as a {@link List}.

* the supplied {@link List} of {@code arguments}.

(same below for other methods)

marcphilipp · 2025-05-26T06:37:01Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	 * @param arguments the arguments as a List to be used for an invocation
+	 * of the test method; must not be {@code null} but may contain {@code null}


Suggested change

* @param arguments the arguments as a List to be used for an invocation

* of the test method; must not be {@code null} but may contain {@code null}

* @param arguments the arguments to be used for an invocation of the test

* method; must not be {@code null} but may contain {@code null}

(same below for other methods)

marcphilipp · 2025-05-26T06:38:32Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	 * Convert the arguments to a new mutable {@link List} containing the same
+	 * elements as {@link #get()}.
+	 *
+	 * <p>This is useful for test logic that benefits from {@code List} operations such as filtering,


Please hard-wrap lines at 80 chars.

marcphilipp · 2025-05-26T06:38:53Z

jupiter-tests/src/test/java/org/junit/jupiter/params/provider/ArgumentsTests.java

@@ -56,4 +60,50 @@ void argumentsReturnsSameArrayUsedForCreating() {
 		assertThat(arguments.get()).isSameAs(input);
 	}

+	@Test
+	void ofSupportsList() {


Suggested change

void ofSupportsList() {

void fromSupportsList() {

marcphilipp · 2025-05-26T06:39:37Z

jupiter-tests/src/test/java/org/junit/jupiter/params/provider/ArgumentsTests.java

+	}
+
+	@Test
+	void argumentsSupportsListAlias() {


Suggested change

void argumentsSupportsListAlias() {

void argumentsFromSupportsList() {

marcphilipp · 2025-05-26T06:40:08Z

jupiter-tests/src/test/java/org/junit/jupiter/params/provider/ArgumentsTests.java

+
+		assertThat(result).containsExactly("a", 2, null); // preserves content
+		result.add("extra"); // confirms mutability
+		assertThat(result).contains("extra");


Please also verify that the array in arguments can't be modified.

marcphilipp · 2025-05-26T06:40:25Z

jupiter-tests/src/test/java/org/junit/jupiter/params/provider/ArgumentsTests.java

+
+	@Test
+	void toListWorksOnEmptyArguments() {
+		Arguments arguments = Arguments.from(Arrays.asList());


Suggested change

Arguments arguments = Arguments.from(Arrays.asList());

Arguments arguments = Arguments.of();

marcphilipp · 2025-05-26T06:40:44Z

jupiter-tests/src/test/java/org/junit/jupiter/params/provider/ArgumentsTests.java

+
+	@Test
+	void toListReturnsMutableListOfArguments() {
+		Arguments arguments = Arguments.from(Arrays.asList("a", 2, null));


Suggested change

Arguments arguments = Arguments.from(Arrays.asList("a", 2, null));

Arguments arguments = Arguments.of("a", 2, null);

marcphilipp · 2025-05-26T06:41:16Z

jupiter-tests/src/test/java/org/junit/jupiter/params/provider/ArgumentsTests.java

+		List<Object> input = Arrays.asList(1, "two", null, 3.0);
+		Arguments arguments = Arguments.from(input);
+
+		assertArrayEquals(new Object[] { 1, "two", null, 3.0 }, arguments.get());


Please add an assertion verifying that modifying the initial List has no effect on arguments

sbrannen · 2025-05-28T11:14:33Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	 * @param arguments the arguments to be used for an invocation of the test
+	 * method; must not be {@code null} but may contain {@code null}.
+	 * @return an instance of {@code Arguments}; never {@code null}.
+	 * @since 6.0


Suggested change

* @param arguments the arguments to be used for an invocation of the test

* method; must not be {@code null} but may contain {@code null}.

* @return an instance of {@code Arguments}; never {@code null}.

* @since 6.0

* @param arguments the arguments to be used for an invocation of the test

* method; must not be {@code null} but may contain {@code null}

* @return an instance of {@code Arguments}; never {@code null}

* @since 6.0

sbrannen · 2025-05-28T11:14:48Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	 * @param arguments the arguments to be used for an invocation of the test
+	 * method; must not be {@code null} but may contain {@code null}.
+	 * @return an instance of {@code Arguments}; never {@code null}.


Suggested change

* @param arguments the arguments to be used for an invocation of the test

* method; must not be {@code null} but may contain {@code null}.

* @return an instance of {@code Arguments}; never {@code null}.

* @param arguments the arguments to be used for an invocation of the test

* method; must not be {@code null} but may contain {@code null}

* @return an instance of {@code Arguments}; never {@code null}

sbrannen · 2025-05-28T11:15:09Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	 * @param name the name of the argument set; must not be {@code null}
+	 * or blank.
+	 * @param arguments the arguments to be used for an invocation of the test
+	 * method; must not be {@code null} but may contain {@code null}.
+	 * @return an {@code ArgumentSet}; never {@code null}.


Suggested change

* @param name the name of the argument set; must not be {@code null}

* or blank.

* @param arguments the arguments to be used for an invocation of the test

* method; must not be {@code null} but may contain {@code null}.

* @return an {@code ArgumentSet}; never {@code null}.

* @param name the name of the argument set; must not be {@code null}

* or blank

* @param arguments the arguments to be used for an invocation of the test

* method; must not be {@code null} but may contain {@code null}

* @return an {@code ArgumentSet}; never {@code null}

sbrannen · 2025-05-28T11:15:52Z

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java

+	 * @return a mutable List of arguments; never {@code null} but may contain
+	 * {@code null}.


Suggested change

* @return a mutable List of arguments; never {@code null} but may contain

* {@code null}.

* @return a mutable List of arguments; never {@code null} but may contain

* {@code null}

mariokhoury4 force-pushed the arguments-list-support branch 4 times, most recently from 3a32cf8 to 9de99b7 Compare May 24, 2025 23:43

Add List-based support to Arguments API (of, arguments, argumentSet, …

3f3aa29

…toList)

mariokhoury4 force-pushed the arguments-list-support branch from 9de99b7 to 3f3aa29 Compare May 24, 2025 23:47

marcphilipp requested changes May 25, 2025

View reviewed changes

mariokhoury4 force-pushed the arguments-list-support branch from cbde5ed to a2ca294 Compare May 25, 2025 15:45

Address feedback: fix argumentsFrom to unpack List properly, update t…

d566f95

…est accordingly

mariokhoury4 force-pushed the arguments-list-support branch from a2ca294 to d566f95 Compare May 25, 2025 15:50

marcphilipp requested changes May 26, 2025

View reviewed changes

mariokhoury4 and others added 2 commits May 27, 2025 21:49

Address feedback: fix documentation and adding test cases

b73ae11

Merge branch 'main' into arguments-list-support

87ca6b4

sbrannen requested changes May 28, 2025

View reviewed changes

	return new ArgumentSet(name, arguments.toArray(new Object[0]));
	return new ArgumentSet(name, arguments.toArray());

		return Stream.of(arguments(Collections.emptyList()));
		return Stream.of(Arguments.of((Object) Collections.emptyList()));

	* the supplied {@code arguments} as a {@link List}.
	* the supplied {@link List} of {@code arguments}.

		* @param arguments the arguments as a List to be used for an invocation
		* of the test method; must not be {@code null} but may contain {@code null}

	void argumentsSupportsListAlias() {
	void argumentsFromSupportsList() {

	Arguments arguments = Arguments.from(Arrays.asList());
	Arguments arguments = Arguments.of();

	Arguments arguments = Arguments.from(Arrays.asList("a", 2, null));
	Arguments arguments = Arguments.of("a", 2, null);

		* @return a mutable List of arguments; never {@code null} but may contain
		* {@code null}.

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mariokhoury4 commented May 24, 2025

Overview

New additions:

Definition of Done

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sbrannen May 25, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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sbrannen May 25, 2025 •

edited

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