code: package com.beijunyi.parallelgit.filesystem.commands;
  
  import java.io.IOException;
  
  import com.beijunyi.parallelgit.AbstractParallelGitTest;
  import com.beijunyi.parallelgit.filesystem.GitFileSystem;
  import com.beijunyi.parallelgit.filesystem.ParallelGitMergeTest;
  import com.beijunyi.parallelgit.filesystem.commands.GfsMerge.Result;
  import org.eclipse.jgit.lib.ObjectId;
  import org.junit.After;
  import org.junit.Before;
  import org.junit.Test;
  
  import static com.beijunyi.parallelgit.filesystem.Gfs.*;
  import static com.beijunyi.parallelgit.filesystem.commands.GfsMerge.Status.*;
  import static com.beijunyi.parallelgit.utils.BranchUtils.getHeadCommit;
  import static java.nio.file.Files.*;
  import static org.junit.Assert.*;
  
  public class GfsMergeFastForwardTest extends AbstractParallelGitTest implements ParallelGitMergeTest {
  
  
    private GitFileSystem gfs;
  
    @Before
    public void setUp() throws IOException {
      initRepository();
      ObjectId base = commit();
      ObjectId ours = commitToBranch(OURS, base);
      writeToCache("/their_file.txt");
      commitToBranch(THEIRS, ours);
      gfs = newFileSystem(OURS, repo);
    }
  
    @After
    public void tearDown() throws IOException {
      if(gfs != null) {
        gfs.close();
        gfs = null;
      }
    }
  
    @Test
    public void mergeWhenHeadIsBehindSourceBranch_theStatusShouldBeFastForward() throws IOException {
      Result result = merge(gfs).source(THEIRS).execute();
  
      assertTrue(result.isSuccessful());
      assertEquals(FAST_FORWARD, result.getStatus());
    }
  
    @Test
    public void mergeWhenHeadIsBehindWithNonConflictingLocalChanges_theStatusShouldBeFastForward() throws IOException {
      write(gfs.getPath("/some_file.txt"), someBytes());
      Result result = merge(gfs).source(THEIRS).execute();
  
      assertTrue(result.isSuccessful());
      assertEquals(FAST_FORWARD, result.getStatus());
    }
  
    @Test
    public void whenFastForwardSucceedWithNewCommit_theResultCommitShouldBeTheHeadOfSourceBranch() throws IOException {
      Result result = merge(gfs).source(THEIRS).execute();
  
      assertTrue(result.isSuccessful());
      assertEquals(FAST_FORWARD, result.getStatus());
      assertEquals(getHeadCommit(THEIRS, repo), result.getCommit());
    }
  
    @Test
    public void mergeWhenHeadIsBehindWithNonConflictingLocalChanges_localChangesShouldBeKept() throws IOException {
      write(gfs.getPath("/test_file.txt"), someBytes());
      Result result = merge(gfs).source(THEIRS).execute();
  
      assertTrue(result.isSuccessful());
      assertTrue(exists(gfs.getPath("/test_file.txt")));
    }
  
    @Test
    public void mergeWhenHeadIsBehindWithConflictingLocalChanges_theStatusShouldBeCheckoutConflict() throws IOException {
      write(gfs.getPath("/their_file.txt"), someBytes());
      Result result = merge(gfs).source(THEIRS).execute();
  
      assertFalse(result.isSuccessful());
      assertEquals(CHECKOUT_CONFLICT, result.getStatus());
    }
  
    @Test
    public void mergeWhenHeadIsBehindWithSquashOption_theResultShouldBeForwardSquashed() throws IOException {
      clearCache();
      writeSomethingToCache();
      commitToBranch(THEIRS);
      Result result = merge(gfs).source(THEIRS).squash(true).execute();
  
      assertTrue(result.isSuccessful());
      assertNull(result.getCommit());
      assertEquals(FAST_FORWARD_SQUASHED, result.getStatus());
    }
  
  
  
  }
  