add proper unit test

tests/unit/test.typ

@@ -3,5 +3,42 @@
 // the output is not relevant for this test
 #set page(width: 0pt, height: 0pt)
 
-// TODO add actual tests
-// #assert.eq(...)
+#let execution = {
+  import stack-pointer: *
+
+  // 1: int main() {
+  // 2:   int x = foo();
+  // 3:   return 0;
+  // 4: }
+  // 5
+  // 6: int foo() {
+  // 7:   return 0;
+  // 8: }
+
+  execute({
+    let foo() = func("foo", 6, l => {
+      l(0)
+      l(1); retval(0)  // (1)
+    })
+    let main() = func("main", 1, l => {
+      l(0)
+      l(1)
+      let (x, ..rest) = foo(); rest  // (2)
+      l(1, push("x", x))
+      l(2)
+    })
+    main(); l(none)
+  })
+};
+
+#let step(line, stack) = (step: (line: line), state: (stack: stack))
+
+#assert.eq(execution, (
+  step(1, ((name: "main", vars: (:)),)),
+  step(2, ((name: "main", vars: (:)),)),
+  step(6, ((name: "main", vars: (:)), (name: "foo", vars: (:)))),
+  step(7, ((name: "main", vars: (:)), (name: "foo", vars: (:)))),
+  step(2, ((name: "main", vars: (x: 0)),)),
+  step(3, ((name: "main", vars: (x: 0)),)),
+  step(none, ()),
+))