Add failing test of hunk-header-style 'file' attribute

Ref #309

src/parse_style.rs

@@ -241,6 +241,8 @@ fn parse_ansi_term_style(
             style.is_strikethrough = true;
         } else if word == "ul" || word == "underline" {
             style.is_underline = true;
+        } else if word == "file" {
+            // Ignore without error: this is meaningful in hunk-header-style.
         } else if !seen_foreground {
             if word == "syntax" {
                 is_syntax_highlighted = true;

src/tests/test_example_diffs.rs

@@ -1008,6 +1008,27 @@ src/align.rs
         assert!(output.contains("@@ -71,11 +71,8 @@ impl<'a> Alignment<'a> {"));
     }
 
+    #[test]
+    fn test_hunk_header_style_with_file() {
+        let config = integration_test_utils::make_config_from_args(&[
+            "--file-style",
+            "yellow",
+            "--hunk-header-style",
+            "file red",
+        ]);
+        let output = integration_test_utils::run_delta(GIT_DIFF_SINGLE_HUNK, &config);
+
+        ansi_test_utils::assert_line_has_style(
+            &output,
+            11,
+            "src/align.rs: impl<'a> Alignment<'a> {",
+            "yellow",
+            &config,
+        );
+        let output = strip_ansi_codes(&output);
+        assert!(output.contains("src/align.rs: impl<'a> Alignment<'a> {"));
+    }
+
     #[test]
     fn test_commit_style_with_color_only_has_style() {
         let config = integration_test_utils::make_config_from_args(&[