Add more test cases for diff()

Author: petetomasik

e2e/diff-output-realistic

@@ -0,0 +1,5 @@
+normal/path.go
+"path/with\tescape.go"
+directory/File Name With Spaces.md
+"projects/17_\360\237\252\201_emoji.py"
+another dir/some file.txt

e2e/multiple-paths

@@ -1,2 +1,3 @@
 user-service/infrastructure/cloudfront.yaml
+user-service/my config/settings.yaml
 user-service/serverless.yaml

pipeline_test.go

@@ -108,13 +108,29 @@ func TestDiff(t *testing.T) {
 func TestDiffWithSubshell(t *testing.T) {
 	want := []string{
 		"user-service/infrastructure/cloudfront.yaml",
+		"user-service/my config/settings.yaml",
 		"user-service/serverless.yaml",
 	}
 	got, err := diff("cat e2e/multiple-paths")
 	assert.NoError(t, err)
 	assert.Equal(t, want, got)
 }
 
+func TestDiffRealisticGitOutput(t *testing.T) {
+	// Fixture mirrors git diff --name-only output: plain paths, C-style
+	// quoted paths (tab, octal emoji), and paths with spaces.
+	want := []string{
+		"normal/path.go",
+		"path/with\tescape.go",
+		"directory/File Name With Spaces.md",
+		"projects/17_🪁_emoji.py",
+		"another dir/some file.txt",
+	}
+	got, err := diff("cat e2e/diff-output-realistic")
+	assert.NoError(t, err)
+	assert.Equal(t, want, got)
+}
+
 func TestDiffWithQuotedPaths(t *testing.T) {
 	want := []string{
 		"projects/test/pages/17_🪁_testfile.py",
@@ -161,6 +177,48 @@ func TestDiffWithSpacesInFilenamesSingleFile(t *testing.T) {
 	assert.Equal(t, want, got)
 }
 
+func TestDiffEmptyOutput(t *testing.T) {
+	got, err := diff(`printf ''`)
+	assert.NoError(t, err)
+	assert.Equal(t, []string{}, got)
+}
+
+func TestDiffWhitespaceOnlyOutput(t *testing.T) {
+	got, err := diff(`printf '\n\n\n'`)
+	assert.NoError(t, err)
+	assert.Equal(t, []string{}, got)
+}
+
+func TestDiffSingleFileNoTrailingNewline(t *testing.T) {
+	// Legacy compat: custom diff commands may not emit a trailing newline
+	want := []string{"services/foo/serverless.yml"}
+	got, err := diff(`printf 'services/foo/serverless.yml'`)
+	assert.NoError(t, err)
+	assert.Equal(t, want, got)
+}
+
+func TestDiffWindowsLineEndings(t *testing.T) {
+	want := []string{
+		"services/foo/file.go",
+		"services/bar/file.go",
+	}
+	got, err := diff(`printf 'services/foo/file.go\r\nservices/bar/file.go\r\n'`)
+	assert.NoError(t, err)
+	assert.Equal(t, want, got)
+}
+
+func TestDiffQuotedPathsWithSpaces(t *testing.T) {
+	// Git C-style quotes paths with special chars; spaces alone don't trigger quoting,
+	// but paths with both spaces and special chars will be quoted.
+	want := []string{
+		"projects/my docs/17_🪁_file.py",
+		"normal/file.txt",
+	}
+	got, err := diff(`printf '"projects/my docs/17_\360\237\252\201_file.py"\nnormal/file.txt\n'`)
+	assert.NoError(t, err)
+	assert.Equal(t, want, got)
+}
+
 func TestStepsToTriggerWithEmojiPaths(t *testing.T) {
 	watch := []WatchConfig{
 		{