Add UT for cache in FilteredProjectDependencyGraphTest (#2394)

Author: slawekjaranowski

impl/maven-core/src/test/java/org/apache/maven/graph/FilteredProjectDependencyGraphTest.java

@@ -0,0 +1,81 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.graph;
+
+import java.util.List;
+
+import org.apache.maven.execution.ProjectDependencyGraph;
+import org.apache.maven.project.MavenProject;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class FilteredProjectDependencyGraphTest {
+
+    @Mock
+    private ProjectDependencyGraph projectDependencyGraph;
+
+    private final MavenProject aProject = createProject("A");
+
+    private final MavenProject bProject = createProject("B");
+
+    private final MavenProject cProject = createProject("C");
+
+    @ParameterizedTest
+    @ValueSource(booleans = {true, false})
+    void downstreamProjectsShouldBeCached(boolean transitive) {
+        FilteredProjectDependencyGraph graph =
+                new FilteredProjectDependencyGraph(projectDependencyGraph, List.of(aProject));
+
+        when(projectDependencyGraph.getDownstreamProjects(bProject, transitive)).thenReturn(List.of(cProject));
+
+        graph.getDownstreamProjects(bProject, transitive);
+        graph.getDownstreamProjects(bProject, transitive);
+
+        verify(projectDependencyGraph).getDownstreamProjects(bProject, transitive);
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {true, false})
+    void upstreamProjectsShouldBeCached(boolean transitive) {
+        FilteredProjectDependencyGraph graph =
+                new FilteredProjectDependencyGraph(projectDependencyGraph, List.of(aProject));
+
+        when(projectDependencyGraph.getUpstreamProjects(bProject, transitive)).thenReturn(List.of(cProject));
+
+        graph.getUpstreamProjects(bProject, transitive);
+        graph.getUpstreamProjects(bProject, transitive);
+
+        verify(projectDependencyGraph).getUpstreamProjects(bProject, transitive);
+    }
+
+    private static MavenProject createProject(String id) {
+        MavenProject result = new MavenProject();
+        result.setGroupId("org.apache");
+        result.setArtifactId(id);
+        result.setVersion("1.2");
+        return result;
+    }
+}