projects.add(project1);
        MavenProject project2 = createProject("groupId", "artifactId2", "1.0");
        projects.add(project2);
        project1.getDependencies().add(createDependency(project2));

        projects = new ProjectSorter(projects).getSortedProjects();

        assertEquals(project2, projects.get(0));
        assertEquals(project1, projects.get(1));
    }

    @Test

        assertEquals(1, ex1.getResults().size());
        MavenProject project1 = ex1.getResults().get(0).getProject();
        assertNotNull(project1);
        assertEquals("testArtifactMissingVersion", project1.getArtifactId());
        assertEquals(pomFile, project1.getFile());

        // multi projects build entry point
        ProjectBuildingException ex2 = assertThrows(
                ProjectBuildingException.class,

import org.apache.maven.project.CycleDetectedException;
import org.apache.maven.project.DuplicateProjectException;
import org.apache.maven.project.MavenProject;
import org.apache.maven.project.ProjectBuildingException;
import org.apache.maven.project.collector.MultiModuleCollectionStrategy;
import org.apache.maven.project.collector.PomlessCollectionStrategy;
import org.apache.maven.project.collector.RequestPomCollectionStrategy;

        ProjectBuildingRequest request = newBuildingRequest();
        request.setLocalRepository(getLocalRepository());
        request.setActiveProfileIds(List.of("profile1"));

        MavenProject project = projectBuilder.build(testPom, request).getProject();

        String id = project.getGroupId() + ":" + project.getArtifactId() + ":" + project.getVersion();

        implementation(projects.mockwebserver3)
        implementation(projects.mockwebserver3Junit4)
        implementation(projects.mockwebserver3Junit5)
        implementation(projects.mockwebserver)
        implementation(projects.loggingInterceptor)
        implementation(projects.okhttpBrotli)
        implementation(projects.okhttpDnsoverhttps)

            throws DuplicateProjectException {
        Map<String, MavenProject> index = new LinkedHashMap<>();
        Map<String, List<File>> collisions = new LinkedHashMap<>();

        for (MavenProject project : projects) {
            String projectId = ArtifactUtils.key(project.getGroupId(), project.getArtifactId(), project.getVersion());

            if (projects != null) {
                Map<String, Map<String, Map<String, MavenProject>>> map = new HashMap<>();
                projects.forEach(project -> map.computeIfAbsent(project.getGroupId(), k -> new HashMap<>())
                        .computeIfAbsent(project.getArtifactId(), k -> new HashMap<>())
                        .put(project.getVersion(), project));
                this.projects = map;
            } else {

    public void setProjects(List<MavenProject> projects) {
        if (!projects.isEmpty()) {
            MavenProject first = projects.get(0);
            this.currentProject = ThreadLocal.withInitial(() -> first);
            this.topLevelProject = projects.stream()
                    .filter(project -> project.isExecutionRoot())
                    .findFirst()
                    .orElse(first);

            String projectId = getId(project);

            MavenProject conflictingProject = projectMap.put(projectId, project);

            if (conflictingProject != null) {
                throw new DuplicateProjectException(
                        projectId,
                        conflictingProject.getFile(),
                        project.getFile(),
                        "Project '" + projectId + "' is duplicated in the reactor");

    Path getRootDirectory();

    /**
     * Returns project parent project, if any.
     * <p>
     * Note that the model may have a parent defined, but an empty parent
     * project may be returned if the parent comes from a remote repository,
     * as a {@code Project} must refer to a buildable project.
     *
     * @return an optional containing the parent project
     * @see Model#getParent()
     */
    @Nonnull