Named arguments in parameterized tests (#2521)

This commit introduces a `Named` interface, which is used to wrap test arguments and give them names.
Thanks to this, arguments in parameterized tests with `@MethodSource` or `@ArgumentSource` can now have optional names. When the argument is included in the display name of an iteration, this name will be used instead of the value.

Author: juliette-derancourt

documentation/src/docs/asciidoc/release-notes/release-notes-5.8.0-M1.adoc

@@ -83,7 +83,9 @@ on GitHub.
 * Dynamic tests now require less memory thanks to a number of improvements to internal
   data structures.
 * Documented constant values in `org.junit.jupiter.api.parallel.Resources`.
-
+* In parameterized tests with `@MethodSource` or `@ArgumentSource`, arguments can now have
+  optional names. When the argument is included in the display name of an iteration, this
+  name will be used instead of the value.
 
 [[release-notes-5.8.0-M1-junit-vintage]]
 === JUnit Vintage

documentation/src/docs/asciidoc/user-guide/writing-tests.adoc

@@ -1634,6 +1634,20 @@ if they exceed the configured maximum length. The limit is configurable via the
 `junit.jupiter.params.displayname.argument.maxlength` configuration parameter and defaults
 to 512 characters.
 
+When using `@MethodSource` or `@ArgumentSource`, you can give names to arguments. This
+name will be used if the argument is included in the invocation display name, like in
+the example below.
+
+[source,java,indent=0]
+----
+include::{testDir}/example/ParameterizedTestDemo.java[tags=named_arguments]
+----
+
+....
+A parameterized test with named arguments ✔
+├─ 1: An important file ✔
+└─ 2: Another file ✔
+....
 
 [[writing-tests-parameterized-tests-lifecycle-interop]]
 ==== Lifecycle and Interoperability

documentation/src/test/java/example/ParameterizedTestDemo.java

@@ -19,6 +19,7 @@
 import static org.junit.jupiter.params.provider.EnumSource.Mode.EXCLUDE;
 import static org.junit.jupiter.params.provider.EnumSource.Mode.MATCH_ALL;
 
+import java.io.File;
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -39,6 +40,7 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.TestInfo;
 import org.junit.jupiter.api.TestReporter;
@@ -441,4 +443,17 @@ void testWithCustomAggregatorAnnotation(@CsvToPerson Person person) {
 	void testWithCustomDisplayNames(String fruit, int rank) {
 	}
 	// end::custom_display_names[]
+
+	// tag::named_arguments[]
+	@DisplayName("A parameterized test with named arguments")
+	@ParameterizedTest(name = "{index}: {0}")
+	@MethodSource("namedArguments")
+	void testWithNamedArguments(File file) {
+	}
+
+	static Stream<Arguments> namedArguments() {
+		return Stream.of(arguments(Named.of("An important file", new File("path1"))),
+			arguments(Named.of("Another file", new File("path2"))));
+	}
+	// end::named_arguments[]
 }

junit-jupiter-api/src/main/java/org/junit/jupiter/api/Named.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2015-2021 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.jupiter.api;
+
+import static org.apiguardian.api.API.Status.STABLE;
+
+import org.apiguardian.api.API;
+
+/**
+ * {@code Named} is used to wrap an object and give it a name.
+ *
+ * @param <T> the type of the payload
+ */
+@API(status = STABLE, since = "5.8")
+public interface Named<T> {
+
+	static <T> Named<T> of(String name, T payload) {
+		return new Named<T>() {
+			@Override
+			public String getName() {
+				return name;
+			}
+
+			@Override
+			public T getPayload() {
+				return payload;
+			}
+
+			@Override
+			public String toString() {
+				return name;
+			}
+		};
+	}
+
+	String getName();
+
+	T getPayload();
+
+}

junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestExtension.java

@@ -143,8 +143,10 @@ protected static Stream<? extends Arguments> arguments(ArgumentsProvider provide
 
 	private Object[] consumedArguments(Object[] arguments, ParameterizedTestMethodContext methodContext) {
 		int parameterCount = methodContext.getParameterCount();
-		return methodContext.hasAggregator() ? arguments
-				: (arguments.length > parameterCount ? Arrays.copyOf(arguments, parameterCount) : arguments);
+		if (methodContext.hasAggregator()) {
+			return arguments;
+		}
+		return arguments.length > parameterCount ? Arrays.copyOf(arguments, parameterCount) : arguments;
 	}
 
 }

junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestNameFormatter.java

@@ -21,6 +21,7 @@
 import java.util.Arrays;
 import java.util.stream.IntStream;
 
+import org.junit.jupiter.api.Named;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.StringUtils;
 
@@ -56,12 +57,19 @@ String format(int invocationIndex, Object... arguments) {
 	}
 
 	private String formatSafely(int invocationIndex, Object[] arguments) {
-		String pattern = prepareMessageFormatPattern(invocationIndex, arguments);
+		Object[] namedArguments = extractNamedArguments(arguments);
+		String pattern = prepareMessageFormatPattern(invocationIndex, namedArguments);
 		MessageFormat format = new MessageFormat(pattern);
-		Object[] humanReadableArguments = makeReadable(format, arguments);
+		Object[] humanReadableArguments = makeReadable(format, namedArguments);
 		return format.format(humanReadableArguments);
 	}
 
+	private Object[] extractNamedArguments(Object[] arguments) {
+		return Arrays.stream(arguments) //
+				.map(argument -> argument instanceof Named ? ((Named<?>) argument).getName() : argument) //
+				.toArray();
+	}
+
 	private String prepareMessageFormatPattern(int invocationIndex, Object[] arguments) {
 		String result = pattern//
 				.replace(DISPLAY_NAME_PLACEHOLDER, this.displayName)//

junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestParameterResolver.java

@@ -12,7 +12,9 @@
 
 import java.lang.reflect.Executable;
 import java.lang.reflect.Method;
+import java.util.Arrays;
 
+import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.api.extension.ParameterResolutionException;
@@ -60,8 +62,19 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 	@Override
 	public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
 			throws ParameterResolutionException {
+		return this.methodContext.resolve(parameterContext, extractPayloads(this.arguments));
+	}
 
-		return this.methodContext.resolve(parameterContext, this.arguments);
+	@SuppressWarnings("unchecked")
+	private Object[] extractPayloads(Object[] arguments) {
+		return Arrays.stream(arguments) //
+				.map(argument -> {
+					if (argument instanceof Named) {
+						return ((Named<Object>) argument).getPayload();
+					}
+					return argument;
+				}) //
+				.toArray();
 	}
 
 }

junit-jupiter-params/src/test/java/org/junit/jupiter/params/ParameterizedTestIntegrationTests.java

@@ -46,6 +46,7 @@
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.MethodOrderer.OrderAnnotation;
+import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Order;
 import org.junit.jupiter.api.Test;
@@ -625,6 +626,15 @@ private EngineExecutionResults execute(String methodName, Class<?>... methodPara
 				methodParameterTypes);
 		}
 
+		@Test
+		void namedParameters() {
+			execute("namedParameters", String.class).allEvents().assertThatEvents() //
+					.haveAtLeast(1,
+						event(test(), displayName("cool name"), finishedWithFailure(message("parameter value")))) //
+					.haveAtLeast(1,
+						event(test(), displayName("default name"), finishedWithFailure(message("default name"))));
+		}
+
 	}
 
 	@Nested
@@ -1009,6 +1019,12 @@ void streamOfTwoDimensionalObjectArrays(Object[][] array) {
 			fail(Arrays.deepToString(array));
 		}
 
+		@MethodSourceTest
+		@Order(13)
+		void namedParameters(String string) {
+			fail(string);
+		}
+
 		// ---------------------------------------------------------------------
 
 		static Stream<Arguments> emptyMethodSource() {
@@ -1066,6 +1082,10 @@ static Stream<Object[][]> streamOfTwoDimensionalObjectArrays() {
 				new Object[][] { { "five", 6 }, { "seven", 8 } });
 		}
 
+		static Stream<Arguments> namedParameters() {
+			return Stream.of(arguments(Named.of("cool name", "parameter value")), arguments("default name"));
+		}
+
 		// ---------------------------------------------------------------------
 
 		@MethodSourceTest