test(edit): Verify display/from_str behavior

crates/toml_edit/src/document.rs

@@ -111,3 +111,10 @@ impl From<Table> for Document {
         }
     }
 }
+
+#[test]
+#[cfg(feature = "parse")]
+#[cfg(feature = "display")]
+fn default_roundtrip() {
+    Document::default().to_string().parse::<Document>().unwrap();
+}

crates/toml_edit/src/item.rs

@@ -390,3 +390,10 @@ pub fn table() -> Item {
 pub fn array() -> Item {
     Item::ArrayOfTables(ArrayOfTables::new())
 }
+
+#[test]
+#[cfg(feature = "parse")]
+#[cfg(feature = "display")]
+fn string_roundtrip() {
+    value("hello").to_string().parse::<Item>().unwrap();
+}

crates/toml_edit/src/key.rs

@@ -434,3 +434,10 @@ impl<'k> std::fmt::Display for KeyMut<'k> {
         std::fmt::Display::fmt(&self.key, f)
     }
 }
+
+#[test]
+#[cfg(feature = "parse")]
+#[cfg(feature = "display")]
+fn string_roundtrip() {
+    Key::new("hello").to_string().parse::<Key>().unwrap();
+}

crates/toml_edit/src/value.rs

@@ -376,3 +376,10 @@ mod tests {
         assert_eq!(features.to_string(), r#"["node", "mouth"]"#);
     }
 }
+
+#[test]
+#[cfg(feature = "parse")]
+#[cfg(feature = "display")]
+fn string_roundtrip() {
+    Value::from("hello").to_string().parse::<Value>().unwrap();
+}