Update Checkout tests to reset and clean working directory

Checkout tests were originally written under the assumption that git
reset would remove untracked files (reset, as implemented in LibGit2Sharp,
originally mistakenly removed untracked files). This updates the tests
to reset and clean the working directory.

Author: jamill

LibGit2Sharp.Tests/CheckoutFixture.cs

@@ -23,8 +23,9 @@ public void CanCheckoutAnExistingBranch(string branchName)
                 Branch master = repo.Branches["master"];
                 Assert.True(master.IsCurrentRepositoryHead);
 
-                // Hard reset to ensure that working directory, index, and HEAD match
-                repo.Reset(ResetOptions.Hard);
+                // Set the working directory to the current head
+                ResetAndCleanWorkingDirectory(repo);
+
                 Assert.False(repo.Index.RetrieveStatus().IsDirty);
 
                 Branch branch = repo.Branches[branchName];
@@ -55,8 +56,9 @@ public void CanCheckoutAnExistingBranchByName(string branchName)
                 Branch master = repo.Branches["master"];
                 Assert.True(master.IsCurrentRepositoryHead);
 
-                // Hard reset to ensure that working directory, index, and HEAD match
-                repo.Reset(ResetOptions.Hard);
+                // Set the working directory to the current head
+                ResetAndCleanWorkingDirectory(repo);
+
                 Assert.False(repo.Index.RetrieveStatus().IsDirty);
 
                 Branch test = repo.Checkout(branchName);
@@ -84,8 +86,9 @@ public void CanCheckoutAnArbitraryCommit(string commitPointer)
                 Branch master = repo.Branches["master"];
                 Assert.True(master.IsCurrentRepositoryHead);
 
-                // Hard reset to ensure that working directory, index, and HEAD match
-                repo.Reset(ResetOptions.Hard);
+                // Set the working directory to the current head
+                ResetAndCleanWorkingDirectory(repo);
+
                 Assert.False(repo.Index.RetrieveStatus().IsDirty);
 
                 Branch detachedHead = repo.Checkout(commitPointer);
@@ -197,8 +200,9 @@ public void CanForcefullyCheckoutWithStagedChanges()
                 Branch master = repo.Branches["master"];
                 Assert.True(master.IsCurrentRepositoryHead);
 
-                // Hard reset to ensure that working directory, index, and HEAD match
-                repo.Reset(ResetOptions.Hard);
+                // Set the working directory to the current head
+                ResetAndCleanWorkingDirectory(repo);
+
                 Assert.False(repo.Index.RetrieveStatus().IsDirty);
 
                 // Add local change
@@ -335,5 +339,19 @@ private void PopulateBasicRepository(Repository repo)
 
             repo.CreateBranch(otherBranchName);
         }
+
+        /// <summary>
+        /// Reset and clean current working directory. This will ensure that the current
+        /// working directory matches the current Head commit.
+        /// </summary>
+        /// <param name="repo">Repository whose current working directory should be operated on.</param>
+        private void ResetAndCleanWorkingDirectory(Repository repo)
+        {
+            // Reset the index and the working tree.
+            repo.Reset(ResetOptions.Hard);
+
+            // Remove untracked files.
+            repo.Index.CleanWorkingDirectory();
+        }
     }
 }