Add integration test skeleton

tests/integration.rs

@@ -0,0 +1,21 @@
+// filename: tests/integration.rs
+
+
+mod integration {
+    use std::process::Command;
+
+    static WITHOUT_ARGS_OUTPUT: &'static str = " USAGE:
+        carman [FLAGS] [OPTIONS] <URL>
+    For more information try --help
+    ";
+
+    #[test]
+    fn calling_carman_without_args() {
+        let output = Command::new("./target/debug/carman")
+            .output()
+            .expect("failed to execute process");
+    
+        assert_eq!(String::from_utf8_lossy(&output.stderr), WITHOUT_ARGS_OUTPUT);
+    }
+    
+}