Add failing test of hunk header with file and no frag

Ref #309

src/tests/test_example_diffs.rs

@@ -1036,6 +1036,28 @@ src/align.rs: impl<'a> Alignment<'a> { │
 "
         ));
     }
+
+    #[test]
+    fn test_hunk_header_style_with_file_no_frag() {
+        let config = integration_test_utils::make_config_from_args(&[
+            "--file-style",
+            "yellow",
+            "--hunk-header-style",
+            "file red",
+            "--hunk-header-decoration-style",
+            "box",
+        ]);
+        let output = integration_test_utils::run_delta(GIT_DIFF_SINGLE_HUNK_NO_FRAG, &config);
+
+        ansi_test_utils::assert_line_has_style(&output, 5, "src/delta.rs", "yellow", &config);
+        let output = strip_ansi_codes(&output);
+        assert!(output.contains(
+            "
+─────────────┐
+src/delta.rs │
+─────────────┘
+"
+        ));
     }
 
     #[test]
@@ -1492,6 +1514,18 @@ index 8e37a9e..6ce4863 100644
                          parent: left,
 ";
 
+    const GIT_DIFF_SINGLE_HUNK_NO_FRAG: &str = "\
+diff --git a/src/delta.rs b/src/delta.rs
+index e401e269..e5304e01 100644
+--- a/src/delta.rs
++++ b/src/delta.rs
+@@ -1,4 +1,3 @@
+-use std::borrow::Cow;
+ use std::fmt::Write as FmtWrite;
+ use std::io::BufRead;
+ use std::io::Write;
+";
+
     const GIT_DIFF_SINGLE_HUNK_WITH_ANSI_ESCAPE_SEQUENCES: &str = "\
 commit 94907c0f136f46dc46ffae2dc92dca9af7eb7c2e
 Author: Dan Davison <dandavison7@gmail.com>