Set<MavenProject> result = new LinkedHashSet<>();
        for (ProjectSegment projectBuild : projectBuilds) {
            if (projectDependencyGraph
                    .getUpstreamProjects(projectBuild.getProject(), false)
                    .isEmpty()) {
                result.add(projectBuild.getProject());
            }
        }
        if (result.isEmpty() && !projectBuilds.isEmpty()) {

            }
        }
    }

    @Override
    public List<MavenProject> getUpstreamProjects(MavenProject project, boolean transitive) {
        Objects.requireNonNull(project, "project cannot be null");

        Set<String> projectIds = new HashSet<>();

        getUpstreamProjects(ProjectSorter.getId(project), projectIds, transitive);

        return getSortedProjects(projectIds);
    }

        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) {

    @Test
    void testADependencies() {
        final List<MavenProject> mavenProjects = stub.getUpstreamProjects(ProjectDependencyGraphStub.A, false);
        assertEquals(0, mavenProjects.size());
    }

    @Test
    void testBDependencies() {
        final List<MavenProject> bProjects = stub.getUpstreamProjects(ProjectDependencyGraphStub.B, false);
        assertEquals(1, bProjects.size());
        assertTrue(

            cache.put(key, list);
        }
        return list;
    }

    @Override
    public List<MavenProject> getUpstreamProjects(MavenProject project, boolean transitive) {
        Key key = new Key(project, transitive, true);
        // Do not use computeIfAbsent here, as the computation is recursive

        final ProjectDependencyGraph dependencyGraph = getSession().getProjectDependencyGraph();
        nonTransitiveUpstreamProjects = dependencyGraph.getUpstreamProjects(getProject(), false);
        transitiveUpstreamProjects = dependencyGraph.getUpstreamProjects(getProject(), true);
    }

    public MavenSession getSession() {
        return session;
    }

    public MavenProject getProject() {

     *            upstream projects.
     * @return The upstream projects in the build order, never {@code null}.
     */
    List<MavenProject> getUpstreamProjects(MavenProject project, boolean transitive);

        for (Dependency dependency : getDependencies()) {
            dependency.addIfDownstream(project, result);
        }
        return result;
    }

    @Override
    public List<MavenProject> getUpstreamProjects(MavenProject project, boolean transitive) {
        List<MavenProject> result = new ArrayList<>();
        final List<Dependency> dependencies = getDependencies();
        for (Dependency dependency : dependencies) {

    void testGetUpstreamProjects() throws CycleDetectedException, DuplicateProjectException {
        ProjectDependencyGraph graph = threeProjectsDependingOnASingle();
        final List<MavenProject> downstreamProjects = graph.getUpstreamProjects(depender1, true);
        assertEquals(aProject, downstreamProjects.get(0));
    }

    private ProjectDependencyGraph threeProjectsDependingOnASingle()

            Set<MavenProject> projectsSet = new HashSet<>(projects);

            for (MavenProject project : projects) {
                if (makeUpstream) {
                    projectsSet.addAll(graph.getUpstreamProjects(project, true));
                }
                if (makeDownstream) {
                    projectsSet.addAll(graph.getDownstreamProjects(project, true));
                }
            }