chore: migrate to Rust edition 2021

 A logical choice now, since our dependencies also require Rust 1.56, for edition 2021, and in a previous commit, the MSRV was set to 1.56 already.

Cargo.toml

@@ -2,7 +2,7 @@
 name = "parameterized"
 version = "1.0.1"
 authors = ["Martijn Gribnau <[email protected]>"]
-edition = "2018"
+edition = "2021"
 license = "MIT OR Apache-2.0"
 description = "Procedural macro which brings a compact parameterized testing implementation to Rust (inspired by JUnit @ParameterizedTest)"
 documentation = "https://docs.rs/crate/parameterized"

src/lib.rs

@@ -84,5 +84,17 @@ mod tests {
 
             Ok(())
         }
+
+        #[pm(v = {
+            Ok(1),
+            // Err("Oh noes".to_string()), // Implements Termination, and reports the exit code: ExitCode::FAILURE, causing the test to fail! Uncomment line to see the result
+        })]
+        fn readme_example(v: Result<u32, String>) -> Result<(), String> {
+            let value = v?; // Can use the question mark operator here, since return type is Result, which implements the Termination trait
+
+            assert_eq!(value, 1);
+
+            Ok(())
+        }
     }
 }