fix: assert_matches macro can only be used in nightly

Cargo.toml

@@ -1,10 +1,13 @@
 [package]
+edition = "2021"
 name = "testing-in-rust"
 version = "0.1.0"
-edition = "2021"
 
 [dependencies]
 colored = "2"
 reqwest = { version = "0.11" }
 tokio = { version = "1", features = ["full"] }
-warp = "0.3"
+warp = "0.3"
+
+[features]
+nightly = []

src/example07/mod.rs

@@ -21,6 +21,7 @@ fn function_returning_an_error(error: CustomError) -> Result<(), CustomError> {
 
 #[cfg(test)]
 mod tests {
+    #[cfg(feature = "nightly")]
     use std::assert_matches::assert_matches;
 
     use crate::example07::{function_returning_an_error, CustomError};
@@ -45,13 +46,15 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "nightly")]
     fn test_function_returning_parse_error_with_assert_matches_macro() {
         let result = function_returning_an_error(CustomError::ParseError("error".to_string()));
 
         assert_matches!(result.unwrap_err(), CustomError::ParseError(_error));
     }
 
     #[test]
+    #[cfg(feature = "nightly")]
     fn test_function_returning_parse_error_with_assert_matches_macro_v2() {
         let result = function_returning_an_error(CustomError::ParseError("error".to_string()));
 

src/lib.rs

@@ -1,4 +1,4 @@
-#![feature(assert_matches)]
+#![cfg_attr(feature = "nightly", feature(assert_matches))]
 pub mod example01;
 pub mod example02;
 pub mod example03;