* @param artifactFile artifact file.
     * @param artifactClassifier artifact classifier.
     */
    void attachArtifact(MavenProject project, File artifactFile, String artifactClassifier);

    /**
     * * See {@link #attachArtifact(MavenProject, String, String, java.io.File)}, but with classifier set to null.
     * @param project project reference.
     * @param artifactType artifact type.

    @Nonnull
    String getGroupId();

    /**
     * {@return the identifier of the artifact}.
     */
    @Nonnull
    String getArtifactId();

    /**
     * Returns the classifier of the artifact.
     *
     * @return the classifier or an empty string if none, never {@code null}
     */
    @Nonnull
    String getClassifier();

    /**

            String groupId,
            String artifactId,
            VersionRange versionRange,
            String type,
            String classifier,
            String scope,
            boolean optional) {
        return createArtifactX(groupId, artifactId, versionRange, type, classifier, scope, null, optional);
    }

    private Artifact createProjectArtifactX(String groupId, String artifactId, String version) {

     */
    @Nonnull
    String getExtension();

    /**
     * Get the default classifier associated to the dependency type.
     * The default classifier can be overridden when specifying
     * the {@link Dependency#getClassifier()}.
     *
     * @return the default classifier, or {@code null}.
     */
    @Nullable
    String getClassifier();

    /**

     * @param artifactId the artifact identifier, or {@code null} is unspecified
     * @param version the artifact version, or {@code null} is unspecified
     * @param classifier the artifact classifier, or {@code null} is unspecified
     * @param extension the artifact extension, or {@code null} is unspecified
     * @param type the artifact type, or {@code null} is unspecified

            metadata.setPlugins(new ArrayList<>(recessive.getPlugins()));
        }

        artifacts.clear();
    }

    private String getKey(String classifier, String extension) {
        return classifier + ':' + extension;
    }

    @Override
    public String getGroupId() {
        return metadata.getGroupId();
    }

    @Override
    public String getArtifactId() {

            for (Dependency dependency : project.getDependencies()) {
                String classifier = dependency.getClassifier();
                if (classifier == null) {
                    ArtifactType type = stereotypes.get(dependency.getType());
                    if (type != null) {
                        classifier = type.getClassifier();
                    }
                }

    /**
     * Gets the type of the constituent's artifact.
     *
     * @return The type, never {@code null}.
     */
    String getType();

    /**
     * Gets the classifier of the constituent's artifact.
     *
     * @return The classifier or an empty string, never {@code null}.
     */
    String getClassifier();

    /**
     * Gets the version of the constituent's artifact.
     *

        when(artifact.getGroupId()).thenReturn("group1");
        when(artifact.getArtifactId()).thenReturn("artifact1");
        when(artifact.getExtension()).thenReturn("ext");
        when(artifact.getClassifier()).thenReturn("classifier1");
        when(artifact.getVersion()).thenReturn("1");
        artifacts.add(artifact);

        Artifact artifact2 = mock(Artifact.class);
        when(artifact2.getFile()).thenReturn(null);

      <fields>
        <field>
          <name>classifier</name>
          <version>1.1.0+</version>
          <type>String</type>
          <description>The classifier of the sub-artifact. Each classifier and extension pair may only appear once.</description>
          <defaultValue></defaultValue>
          <identifier>true</identifier>