run-make-support: improve docs for assert_exit_code

Author: jieyouxu

Diff for: src/tools/run-make-support/src/command.rs

@@ -388,9 +388,13 @@ impl CompletedProcess {
         self
     }
 
+    /// Check the **exit status** of the process. On Unix, this is *not* the **wait status**.
+    ///
+    /// See [`std::process::ExitStatus::code`]. This is not to be confused with
+    /// [`std::process::ExitCode`].
     #[track_caller]
     pub fn assert_exit_code(&self, code: i32) -> &Self {
-        assert!(self.output.status.code() == Some(code));
+        assert_eq!(self.output.status.code(), Some(code));
         self
     }
 }