modtime:   htmlModTime,
			reqHeader: map[string]string{
				"If-Modified-Since": htmlModTime.UTC().Format(TimeFormat),
			},
			wantStatus: 304,
		},
		"not_modified_modtime_with_contenttype": {
			file:             "testdata/style.css",
			serveContentType: "text/css", // explicit content type
			serveETag:        `"foo"`,    // Last-Modified sent only when no ETag