'Learning Tests' that uses the JGit API to clone existing repositories: http://www.codeaffine.com/2015/11/30/jgit-clone-repository/

CloneLearningTest.java

package com.codeaffine.jgit.example;

import static java.util.Collections.singleton;
import static org.eclipse.jgit.api.ListBranchCommand.ListMode.ALL;
import static org.eclipse.jgit.transport.RemoteConfig.getAllRemoteConfigs;
import static org.junit.Assert.*;

import java.io.File;
import java.io.IOException;
import java.util.List;

import org.eclipse.jgit.api.CloneCommand;
import org.eclipse.jgit.api.Git;
import org.eclipse.jgit.api.errors.GitAPIException;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.transport.RemoteConfig;
import org.junit.After;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TemporaryFolder;

public class CloneLearningTest {

  @Rule
  public TemporaryFolder tempFolder = new TemporaryFolder();

  private Git remote;
  private Git local;
  private CloneCommand cloneCommand;

  @Before
  public void setUp() throws GitAPIException, IOException {
    remote = Git.init().setDirectory( tempFolder.newFolder( "remote" ) ).call();
    remote.commit().setMessage( "Initial commit" ).call();
    cloneCommand = Git.cloneRepository();
  }
  
  @After
  public void tearDown() {
    remote.close();
    local.close();
  }
  
  @Test
  public void testClone() throws Exception {
    File directory = getLocalRepositoryLocation();
    cloneCommand.setURI( getRemoteUrl() );
    cloneCommand.setDirectory( directory );
    
    local = cloneCommand.call();
    
    assertEquals( local.getRepository().getDirectory(), new File( directory, ".git" ) );
    assertEquals( local.getRepository().getWorkTree(), directory );
  }
  
  @Test
  public void testCloneBare() throws Exception {
    File directory = getLocalRepositoryLocation();
    cloneCommand.setBare( true );
    cloneCommand.setURI( getRemoteUrl() );
    cloneCommand.setGitDir( directory );
    
    local = cloneCommand.call();

    assertTrue( local.getRepository().isBare() );
    assertEquals( local.getRepository().getDirectory(), directory );
  }
  
  @Test
  public void testCloneAllBranches() throws Exception {
    remote.commit().setMessage( "initial commit" ).call();
    remote.branchCreate().setName( "extra" ).call();
    cloneCommand.setURI( getRemoteUrl() );
    cloneCommand.setDirectory( getLocalRepositoryLocation() );
    cloneCommand.setCloneAllBranches( true );
    
    local = cloneCommand.call();
    
    Ref ref = local.getRepository().getRef( "refs/remotes/origin/extra" );
    assertTrue( listAllLocalBranches().contains( ref ) );
  }

  @Test
  public void testCloneSpecificBranch() throws Exception {
    remote.commit().setMessage( "initial commit" ).call();
    Ref extraBranch = remote.branchCreate().setName( "extra" ).call();
    cloneCommand.setURI( getRemoteUrl() );
    cloneCommand.setDirectory( getLocalRepositoryLocation() );
    cloneCommand.setBranchesToClone( singleton( extraBranch.getName() ) );

    local = cloneCommand.call();
    
    Ref ref = local.getRepository().getRef( "refs/remotes/origin/extra" );
    assertTrue( listAllLocalBranches().contains( ref ) );
  }
  
  @Test
  public void testCloneNonDefaultRemote() throws Exception {
    cloneCommand.setURI( getRemoteUrl() );
    cloneCommand.setDirectory( getLocalRepositoryLocation() );
    cloneCommand.setRemote( "upstream" );

    local = cloneCommand.call();
    
    List<RemoteConfig> remoteConfigs = getAllRemoteConfigs( local.getRepository().getConfig() );
    assertEquals( 1, remoteConfigs.size() );
    assertEquals( "upstream", remoteConfigs.get( 0 ).getName() );
  }

  private String getRemoteUrl() throws IOException {
    return remote.getRepository().getDirectory().getCanonicalPath();
  }

  private File getLocalRepositoryLocation() throws IOException {
    return tempFolder.newFolder( "local" );
  }

  private List<Ref> listAllLocalBranches() throws GitAPIException {
    return local.branchList().setListMode( ALL ).call();
  }
  
}