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

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;

     * is a prerequisite of the given project.
     *
     * @param project The project whose upstream projects should be retrieved, must not be {@code null}.
     * @param transitive A flag whether to retrieve all direct and indirect upstream projects or just the immediate
     *            upstream projects.

        this(projects, projects);
    }

    /**
     * Creates a new project dependency graph based on the specified projects.
     *
     * @param allProjects All collected projects.
     * @param projects    The projects to create the dependency graph with.
     * @throws DuplicateProjectException
     * @throws CycleDetectedException
     * @since 3.5.0

            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());

        for (MavenProject project : projects) {
            request.setArtifact(new ProjectArtifact(project));
            request.setArtifactDependencies(project.getDependencyArtifacts());
            request.setManagedVersionMap(project.getManagedVersionMap());
            request.setRemoteRepositories(project.getRemoteArtifactRepositories());

            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");

import org.apache.maven.project.MavenProject;
import org.apache.maven.project.ProjectBuilder;
import org.apache.maven.project.ProjectBuildingException;
import org.apache.maven.project.ProjectBuildingRequest;
import org.apache.maven.project.ProjectBuildingResult;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Utility to select projects for a given set of pom.xml files.
 */
@Named

        // compute the projects mapping
        if (projects == null) {
            List<MavenProject> projects = session.getProjects();
            if (projects != null) {
                Map<String, Map<String, Map<String, MavenProject>>> map = new HashMap<>();
                projects.forEach(project -> map.computeIfAbsent(project.getGroupId(), k -> new HashMap<>())

     * @param collisions The POM files of the projects that collided, indexed by their g:a:v, may be {@code null}.
     */
    public DuplicateProjectException(String message, Map<String, List<File>> collisions) {
        super(message, (File) null);

        this.collisions = (collisions != null) ? collisions : new LinkedHashMap<>();
    }

    /**
     * Gets the POM files of the projects that collided.
     *