Add doc(test)s for returning Output

Author: johannhof

Readme.md

@@ -57,6 +57,16 @@ assert_cli::assert_cli("echo", &["42"]).unwrap();
 assert_cli!("echo", &["42"] => Success).unwrap();
 ```
 
+All exported functions and the macro return a `Result` containing the
+`Output` of the process, allowing you to do further custom assertions:
+
+```rust
+#[macro_use] extern crate assert_cli;
+let output = assert_cli!("echo", &["Number 42"] => Success).unwrap();
+let stdout = std::str::from_utf8(&output.stdout).unwrap();
+assert!(stdout.contains("42"));
+```
+
 ## License
 
 Licensed under either of

src/lib.rs

@@ -35,6 +35,18 @@
 //! # }
 //! ```
 //!
+//! All exported functions and the macro return a `Result` containing the
+//! `Output` of the process, allowing you to do further custom assertions:
+//!
+//! ```rust
+//! # #[macro_use] extern crate assert_cli;
+//! # fn main() {
+//! let output = assert_cli!("echo", &["Number 42"] => Success).unwrap();
+//! let stdout = std::str::from_utf8(&output.stdout).unwrap();
+//! assert!(stdout.contains("42"));
+//! # }
+//! ```
+//!
 //! Make sure to include the crate as `#[macro_use] extern crate assert_cli;`.