test(tazjin/rlox): Add a handful of interpreter tests r/2100

Change-Id: I32dd896d42cc73d68d73093e9cbb74b48d95e041
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2386
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

2 files changed, 66 insertions, 0 deletions

diff --git a/users/tazjin/rlox/src/interpreter.rs b/users/tazjin/rlox/src/interpreter.rs
index 744e6ea895..cccc381b32 100644
--- a/users/tazjin/rlox/src/interpreter.rs
+++ b/users/tazjin/rlox/src/interpreter.rs
@@ -8,6 +8,9 @@ use std::sync::RwLock;
 // Implementation of built-in functions.
 mod builtins;
 
+#[cfg(test)]
+mod tests;
+
 // Tree-walk interpreter
 
 // Representation of all callables, including builtins & user-defined
diff --git a/users/tazjin/rlox/src/interpreter/tests.rs b/users/tazjin/rlox/src/interpreter/tests.rs
new file mode 100644
index 0000000000..3aaea707d6
--- /dev/null
+++ b/users/tazjin/rlox/src/interpreter/tests.rs
@@ -0,0 +1,63 @@
+use super::*;
+
+/// Evaluate a code snippet, returning a value.
+fn parse_eval(code: &str) -> Value {
+    let chars: Vec<char> = code.chars().collect();
+    let tokens = scanner::scan(&chars).expect("could not scan code");
+    let program = parser::parse(tokens).expect("could not parse code");
+    Interpreter::create()
+        .interpret(&program)
+        .expect("could not eval code")
+}
+
+#[test]
+fn test_if() {
+    let result = parse_eval(
+        r#"
+if (42 > 23)
+  "pass";
+else
+  "fail";
+"#,
+    );
+
+    assert_eq!(Value::Literal(Literal::String("pass".into())), result);
+}
+
+#[test]
+fn test_scope() {
+    let result = parse_eval(
+        r#"
+var result = "";
+
+var a = "global a, ";
+var b = "global b, ";
+var c = "global c";
+
+{
+  var a = "outer a, ";
+  var b = "outer b, ";
+
+  {
+    var a = "inner a, ";
+    result = a + b + c;
+  }
+}
+"#,
+    );
+
+    assert_eq!(
+        Value::Literal(Literal::String("inner a, outer b, global c".into())),
+        result
+    );
+}
+
+#[test]
+fn test_binary_operators() {
+    assert_eq!(Value::Literal(Literal::Number(42.0)), parse_eval("40 + 2;"));
+
+    assert_eq!(
+        Value::Literal(Literal::String("foobar".into())),
+        parse_eval("\"foo\" + \"bar\";")
+    );
+}