Add first ReplState test

crates/repl_test/src/state.rs

@@ -0,0 +1,27 @@
+use roc_repl_cli::repl_state::{validate, ReplState};
+use rustyline::validate::ValidationResult;
+
+#[test]
+fn one_plus_one() {
+    let mut state = ReplState::new();
+    let input = "1 + 1";
+
+    assert_step(input, &mut state, Ok("2 : Num *   # TODOval1"));
+    assert!(matches!(validate(input), Ok(ValidationResult::Valid(None))));
+}
+
+fn assert_step(input: &str, state: &mut ReplState, expected_step_result: Result<&str, i32>) {
+    match state.step(input) {
+        Ok(string) => {
+            let escaped = std::string::String::from_utf8(
+                strip_ansi_escapes::strip(string.trim()).unwrap().into(),
+            )
+            .unwrap();
+
+            assert_eq!(expected_step_result.map(str::to_string), Ok(escaped));
+        }
+        Err(err) => {
+            assert_eq!(expected_step_result, Err(err));
+        }
+    }
+}