[fine] Many test improvements, error improvements

- Check for more error conditions
- Move to more definitive error assertions
- Simpler error messages in some cases
- Test more conditions more thoroughly, revisit old tests

fine/tests/example_tests.rs

@@ -298,7 +298,7 @@ fn assert_errors(tree: &SyntaxTree, lines: &Lines, expected_errors: Vec<&str>) {
         None,
         expected_errors,
         errors,
-        "expected no errors"
+        "expected error messages to match"
     );
 }