8321124: java/util/stream/GatherersTest.java times out

Reviewed-by: alanb

Author: Viktor Klang

test/jdk/ProblemList.txt

@@ -722,7 +722,6 @@ com/sun/jdi/InvokeHangTest.java                                 8218463 linux-al
 
 java/util/Locale/LocaleProvidersRun.java                        8268379 macosx-x64
 sun/util/locale/provider/CalendarDataRegression.java            8268379 macosx-x64
-java/util/stream/GatherersTest.java                             8321124 generic-all
 
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test/jdk/java/util/stream/GathererTest.java

@@ -349,7 +349,7 @@ public void testCompositionOfStatefulGatherers(Config config) {
     @ParameterizedTest
     @MethodSource("configurations")
     public void testMassivelyComposedGatherers(Config config) {
-        final int ITERATIONS = 512; // Total number of compositions is 1 + (iterations*2)
+        final int ITERATIONS = 256; // Total number of compositions is 1 + (iterations*2)
         Gatherer<Integer,?,Integer> g = addOne;
         for(int i = 0;i < ITERATIONS;++i) {
             g = g.andThen(timesTwo).andThen(addOne);

test/jdk/java/util/stream/GatherersFoldTest.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.util.List;
+import java.util.stream.Gatherers;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assumptions.*;
+
+/**
+ * @test
+ * @summary Tests the API and contract of Gatherers.fold
+ * @enablePreview
+ * @run junit GatherersFoldTest
+ */
+
+public class GatherersFoldTest {
+
+    record Config(int streamSize, boolean parallel) {
+        Stream<Integer> stream() {
+            var stream = Stream.iterate(1, i -> i + 1).limit(streamSize);
+            stream = parallel ? stream.parallel() : stream.sequential();
+            return stream;
+        }
+    }
+
+    static final Stream<Integer> sizes(){
+        return Stream.of(0,1,10,33,99,9999);
+    }
+
+    static final Stream<Config> sequentialAndParallel(int size) {
+        return Stream.of(false, true)
+                .map(parallel ->
+                        new Config(size, parallel));
+    }
+
+    static final Stream<Config> configurations() {
+        return sizes().flatMap(i -> sequentialAndParallel(i));
+    }
+
+    @Test
+    public void throwsNPEWhenStateSupplierIsNull() {
+        assertThrows(NullPointerException.class, () -> Gatherers.<String, String>fold(null, (state, next) -> state));
+    }
+
+    @Test
+    public void throwsNPEWhenFolderFunctionIsNull() {
+        assertThrows(NullPointerException.class, () -> Gatherers.<String, String>fold(() -> "", null));
+    }
+
+    @ParameterizedTest
+    @MethodSource("configurations")
+    public void behavesAsExpected(Config config) {
+        final var expectedResult = List.of(
+            config.stream()
+                    .sequential()
+                    .reduce(0L, (acc, next) -> acc + next,(l, r) -> {
+                        throw new IllegalStateException();
+                    })
+        );
+
+        final var result = config.stream()
+                .gather(Gatherers.fold(() -> 0L, (acc, next) -> acc + next))
+                .toList();
+
+        assertEquals(expectedResult, result);
+    }
+}