diff --git a/src/reader.rs b/src/reader.rs
index 9ad1b91..37b2009 100644
--- a/src/reader.rs
+++ b/src/reader.rs
@@ -44,7 +44,7 @@ use crate::tiff::{Field, ProvideUnit};
 /// let reader = exif::Reader::new(
 ///     &mut std::io::BufReader::new(&file)).unwrap();
 /// let xres = reader.get_field(exif::Tag::XResolution, false).unwrap();
-/// assert_eq!(format!("{}", xres.display_value().with_unit(&reader)),
+/// assert_eq!(xres.display_value().with_unit(&reader).to_string(),
 ///            "72 pixels per inch");
 /// ```
 //
@@ -211,23 +211,23 @@ mod tests {
         let reader = Reader::new(&mut BufReader::new(&file)).unwrap();
         // No unit.
         let exifver = reader.get_field(Tag::ExifVersion, false).unwrap();
-        assert_eq!(format!("{}", exifver.display_value().with_unit(&reader)),
+        assert_eq!(exifver.display_value().with_unit(&reader).to_string(),
                    "2.31");
         // Fixed string.
         let width = reader.get_field(Tag::ImageWidth, false).unwrap();
-        assert_eq!(format!("{}", width.display_value().with_unit(&reader)),
+        assert_eq!(width.display_value().with_unit(&reader).to_string(),
                    "15 pixels");
         // Unit tag (with a non-default value).
         let gpsalt = reader.get_field(Tag::GPSAltitude, false).unwrap();
-        assert_eq!(format!("{}", gpsalt.display_value().with_unit(&reader)),
+        assert_eq!(gpsalt.display_value().with_unit(&reader).to_string(),
                    "0.5 meters below sea level");
         // Unit tag is missing but the default is specified.
         let xres = reader.get_field(Tag::XResolution, false).unwrap();
-        assert_eq!(format!("{}", xres.display_value().with_unit(&reader)),
+        assert_eq!(xres.display_value().with_unit(&reader).to_string(),
                    "72 pixels per inch");
         // Unit tag is missing and the default is not specified.
         let gpslat = reader.get_field(Tag::GPSLatitude, false).unwrap();
-        assert_eq!(format!("{}", gpslat.display_value().with_unit(&reader)),
+        assert_eq!(gpslat.display_value().with_unit(&reader).to_string(),
                    "10 deg 0 min 0 sec [GPSLatitudeRef missing]");
     }
 }
diff --git a/src/tiff.rs b/src/tiff.rs
index 02b420f..4c82090 100644
--- a/src/tiff.rs
+++ b/src/tiff.rs
@@ -168,7 +168,7 @@ pub fn is_tiff(buf: &[u8]) -> bool {
 /// use exif::DateTime;
 /// let dt = DateTime::from_ascii(b"2016:05:04 03:02:01").unwrap();
 /// assert_eq!(dt.year, 2016);
-/// assert_eq!(format!("{}", dt), "2016-05-04 03:02:01");
+/// assert_eq!(dt.to_string(), "2016-05-04 03:02:01");
 /// ```
 #[derive(Debug)]
 pub struct DateTime {
@@ -290,15 +290,15 @@ impl<'a> Field<'a> {
     ///     thumbnail: false,
     ///     value: Value::Short(vec![3]),
     /// };
-    /// assert_eq!(format!("{}", xres.display_value()), "72");
-    /// assert_eq!(format!("{}", cm.display_value()), "cm");
+    /// assert_eq!(xres.display_value().to_string(), "72");
+    /// assert_eq!(cm.display_value().to_string(), "cm");
     /// // The unit of XResolution is indicated by ResolutionUnit.
-    /// assert_eq!(format!("{}", xres.display_value().with_unit(&cm)),
+    /// assert_eq!(xres.display_value().with_unit(&cm).to_string(),
     ///            "72 pixels per cm");
     /// // If ResolutionUnit is not given, the default value is used.
-    /// assert_eq!(format!("{}", xres.display_value().with_unit(())),
+    /// assert_eq!(xres.display_value().with_unit(()).to_string(),
     ///            "72 pixels per inch");
-    /// assert_eq!(format!("{}", xres.display_value().with_unit(&xres)),
+    /// assert_eq!(xres.display_value().with_unit(&xres).to_string(),
     ///            "72 pixels per inch");
     ///
     /// let flen = Field {
@@ -308,8 +308,8 @@ impl<'a> Field<'a> {
     /// };
     /// // The unit of the focal length is always mm, so the argument
     /// // has nothing to do with the result.
-    /// assert_eq!(format!("{}", flen.display_value().with_unit(())), "24 mm");
-    /// assert_eq!(format!("{}", flen.display_value().with_unit(&cm)), "24 mm");
+    /// assert_eq!(flen.display_value().with_unit(()).to_string(), "24 mm");
+    /// assert_eq!(flen.display_value().with_unit(&cm).to_string(), "24 mm");
     /// ```
     #[inline]
     pub fn display_value(&self) -> DisplayValue {
@@ -428,7 +428,7 @@ mod tests {
     fn date_time() {
         let mut dt = DateTime::from_ascii(b"2016:05:04 03:02:01").unwrap();
         assert_eq!(dt.year, 2016);
-        assert_eq!(format!("{}", dt), "2016-05-04 03:02:01");
+        assert_eq!(dt.to_string(), "2016-05-04 03:02:01");
 
         dt.parse_subsec(b"987").unwrap();
         assert_eq!(dt.nanosecond.unwrap(), 987000000);
@@ -479,11 +479,11 @@ mod tests {
             thumbnail: false,
             value: Value::Undefined(b"0231", 0),
         };
-        assert_eq!(format!("{}", exifver.display_value()),
+        assert_eq!(exifver.display_value().to_string(),
                    "2.31");
-        assert_eq!(format!("{}", exifver.display_value().with_unit(())),
+        assert_eq!(exifver.display_value().with_unit(()).to_string(),
                    "2.31");
-        assert_eq!(format!("{}", exifver.display_value().with_unit(&cm)),
+        assert_eq!(exifver.display_value().with_unit(&cm).to_string(),
                    "2.31");
         // Fixed string.
         let width = Field {
@@ -491,11 +491,11 @@ mod tests {
             thumbnail: false,
             value: Value::Short(vec![257]),
         };
-        assert_eq!(format!("{}", width.display_value()),
+        assert_eq!(width.display_value().to_string(),
                    "257");
-        assert_eq!(format!("{}", width.display_value().with_unit(())),
+        assert_eq!(width.display_value().with_unit(()).to_string(),
                    "257 pixels");
-        assert_eq!(format!("{}", width.display_value().with_unit(&cm)),
+        assert_eq!(width.display_value().with_unit(&cm).to_string(),
                    "257 pixels");
         // Unit tag (with a non-default value).
         // Unit tag is missing but the default is specified.
@@ -504,13 +504,13 @@ mod tests {
             thumbnail: false,
             value: Value::Rational(vec![Rational { num: 300, denom: 1 }]),
         };
-        assert_eq!(format!("{}", xres.display_value()),
+        assert_eq!(xres.display_value().to_string(),
                    "300");
-        assert_eq!(format!("{}", xres.display_value().with_unit(())),
+        assert_eq!(xres.display_value().with_unit(()).to_string(),
                    "300 pixels per inch");
-        assert_eq!(format!("{}", xres.display_value().with_unit(&cm)),
+        assert_eq!(xres.display_value().with_unit(&cm).to_string(),
                    "300 pixels per cm");
-        assert_eq!(format!("{}", xres.display_value().with_unit(&cm_tn)),
+        assert_eq!(xres.display_value().with_unit(&cm_tn).to_string(),
                    "300 pixels per inch");
         // Unit tag is missing and the default is not specified.
         let gpslat = Field {
@@ -522,11 +522,11 @@ mod tests {
                 Rational { num: 1, denom: 10 },
             ]),
         };
-        assert_eq!(format!("{}", gpslat.display_value()),
+        assert_eq!(gpslat.display_value().to_string(),
                    "10 deg 0 min 0.1 sec");
-        assert_eq!(format!("{}", gpslat.display_value().with_unit(())),
+        assert_eq!(gpslat.display_value().with_unit(()).to_string(),
                    "10 deg 0 min 0.1 sec [GPSLatitudeRef missing]");
-        assert_eq!(format!("{}", gpslat.display_value().with_unit(&cm)),
+        assert_eq!(gpslat.display_value().with_unit(&cm).to_string(),
                    "10 deg 0 min 0.1 sec [GPSLatitudeRef missing]");
     }
 }
diff --git a/src/value.rs b/src/value.rs
index 9f3bf94..5002c4c 100644
--- a/src/value.rs
+++ b/src/value.rs
@@ -84,11 +84,9 @@ impl<'a> Value<'a> {
     /// ```
     /// use exif::{Value, Tag};
     /// let val = Value::Undefined(b"0231", 0);
-    /// assert_eq!(format!("{}", val.display_as(Tag::ExifVersion)),
-    ///            "2.31");
+    /// assert_eq!(val.display_as(Tag::ExifVersion).to_string(), "2.31");
     /// let val = Value::Short(vec![2]);
-    /// assert_eq!(format!("{}", val.display_as(Tag::ResolutionUnit)),
-    ///            "inch");
+    /// assert_eq!(val.display_as(Tag::ResolutionUnit).to_string(), "inch");
     /// ```
     #[inline]
     pub fn display_as(&self, tag: crate::tag::Tag) -> Display {
diff --git a/tests/rwrcmp.rs b/tests/rwrcmp.rs
index b1a8ae7..040dada 100644
--- a/tests/rwrcmp.rs
+++ b/tests/rwrcmp.rs
@@ -172,7 +172,7 @@ fn compare_field_value(value1: &Value, value2: &Value) {
             assert_eq!(v1, v2),
         (&Value::Double(ref v1), &Value::Double(ref v2)) =>
             assert_eq!(v1, v2),
-        _ => panic!(format!("{:?} != {:?}", value1, value2)),
+        _ => panic!("{:?} != {:?}", value1, value2),
     }
 }