Adds support of commit cherry-picking (#403)

Author: ctabin

src/main/java/org/gitlab4j/api/CommitsApi.java

@@ -644,4 +644,23 @@ public Commit revertCommit(Object projectIdOrPath, String sha, String branch) th
                 "projects", getProjectIdOrPath(projectIdOrPath), "repository", "commits", sha, "revert");
         return (response.readEntity(Commit.class));
     }
+    
+    /**
+     * Cherry picks a commit in a given branch.
+     *
+     * <pre><code>GitLab Endpoint: POST /projects/:id/repository/commits/:sha/cherry_pick</code></pre>
+     *
+     * @since GitLab 8.15
+     * @param projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance
+     * @param sha the commit SHA to cherry pick
+     * @param branch the target branch to cherry pick the commit on
+     * @return a Commit instance holding the cherry picked commit
+     * @throws GitLabApiException GitLabApiException if any exception occurs during execution
+     */
+    public Commit cherryPickCommit(Object projectIdOrPath, String sha, String branch) throws GitLabApiException {
+        GitLabApiForm formData = new GitLabApiForm().withParam("branch", branch, true);
+        Response response = post(Response.Status.CREATED, formData,
+                "projects", getProjectIdOrPath(projectIdOrPath), "repository", "commits", sha, "cherry_pick");
+        return (response.readEntity(Commit.class));
+    }
 }

src/test/java/org/gitlab4j/api/TestCommitsApi.java

@@ -15,6 +15,7 @@
 import java.util.Optional;
 
 import javax.ws.rs.core.Response;
+import org.gitlab4j.api.models.Branch;
 
 import org.gitlab4j.api.models.Comment;
 import org.gitlab4j.api.models.Commit;
@@ -321,4 +322,50 @@ public void testRevertCommit() throws GitLabApiException {
         repoFile = gitLabApi.getRepositoryFileApi().getOptionalFile(testProject, filePath, "master");
         assertFalse(repoFile.isPresent());
     }
+    
+    @Test
+    public void testCherryPickCommit() throws GitLabApiException {
+        
+        // Make sure the branch to cherry pick does not exist
+        if(gitLabApi.getRepositoryApi().getOptionalBranch(testProject, "cherry-pick-branch").isPresent()) {
+           gitLabApi.getRepositoryApi().deleteBranch(testProject, "cherry-pick-branch");
+        }
+        
+        // Make sure the file to create does not exist.
+        String filePath = TEST_CREATE_COMMIT_FILEPATH + ".test";
+        if (gitLabApi.getRepositoryFileApi().getOptionalFile(testProject, filePath, "master").isPresent()) {
+            gitLabApi.getRepositoryFileApi().deleteFile(testProject, filePath, "master", "Deleted test file");
+        }
+
+        // Act
+        Branch branch = gitLabApi.getRepositoryApi().createBranch(testProject, "cherry-pick-branch", "master");
+        
+        // Assert
+        assertNotNull(branch);
+        Optional<RepositoryFile> repoFileBranch = gitLabApi.getRepositoryFileApi().getOptionalFile(testProject, filePath, branch.getName());
+        assertFalse(repoFileBranch.isPresent());
+        
+        // Arrange
+        CommitAction commitAction = new CommitAction()
+                .withAction(Action.CREATE)
+                .withContent("This is the original data in the file")
+                .withFilePath(filePath);
+
+        // Act
+        Commit commit = gitLabApi.getCommitsApi().createCommit(
+                testProject, "master", "Testing createCommit() create action", null, null, null, commitAction);
+
+        // Assert
+        assertNotNull(commit);
+        Optional<RepositoryFile> repoFile = gitLabApi.getRepositoryFileApi().getOptionalFile(testProject, filePath, "master");
+        assertTrue(repoFile.isPresent());
+        
+        // Act
+        Commit cherryPickedCommit = gitLabApi.getCommitsApi().cherryPickCommit(testProject, commit.getId(), "cherry-pick-branch");
+        
+        // Assert
+        assertNotNull(cherryPickedCommit);
+        Optional<RepositoryFile> repoFileBranchCherryPicked = gitLabApi.getRepositoryFileApi().getOptionalFile(testProject, filePath, branch.getName());
+        assertTrue(repoFileBranchCherryPicked.isPresent());
+    }
 }