Add test for return value.

tests/common.rs

@@ -17,6 +17,7 @@ pub fn _run_test(code: &str) -> String {
         debug: false,
         step: false,
         stdout: &mut stdout,
+        parse_only: false,
     };
 
     dilaria::run_program(code, &mut cfg);

tests/functions.rs

@@ -54,6 +54,18 @@ fancy_print("correct");
 "#
 );
 
+run_test!(
+    return_value,
+    r#"
+fn get_value() {
+    return 1;
+}
+
+let x = get_value();
+print x;
+"#
+);
+
 run_test!(
     #[ignore]
     parameters_and_return,

tests/snapshots/functions__return_value.snap

@@ -0,0 +1,5 @@
+---
+source: tests/functions.rs
+expression: output
+---
+"1\n"