[fine] Assignments!

And new error capabilities!

fine/tests/example_tests.rs

@@ -283,6 +283,25 @@ fn assert_eval_ok(tree: &SyntaxTree, lines: &Lines, expected: &str) {
     }
 }
 
+fn assert_errors(tree: &SyntaxTree, lines: &Lines, expected_errors: Vec<&str>) {
+    let semantics = Semantics::new(tree, lines);
+    check(&semantics);
+
+    let errors: Vec<String> = semantics
+        .snapshot_errors()
+        .iter()
+        .map(|e| format!("{}", e))
+        .collect();
+
+    semantic_assert_eq!(
+        &semantics,
+        None,
+        expected_errors,
+        errors,
+        "expected no errors"
+    );
+}
+
 fn assert_check_error(tree: &SyntaxTree, lines: &Lines, expected: &str) {
     let semantics = Semantics::new(tree, lines);
     check(&semantics);