parser-test-best-practices

A set of rules for testing parsers, which are programs that read text and turn it into structured data such as an abstract syntax tree.

In plain words
What is it for?
Use it to structure AST and parser components, create mock fixtures, test parsing separately from AST construction, and write flexible assertions.
Why use it?
It helps parser tests report useful locations and errors while avoiding fragile assertions, circular code dependencies, and mismatched test doubles.

Cursor rule for Cursor

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/consiliency/flutter-structurizr/parser-test-best-practices
Clone the repo
git clone --depth 1 https://github.com/Consiliency/Flutter-Structurizr

Made for: Cursor.

Per session 249 This file is loaded in full into every session.
When invoked 249 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00249 $0.00249
Opus 5 $0.00125 $0.00125
Sonnet 5 $0.00050 $0.00050
Haiku 4.5 $0.00025 $0.00025

Measured 2d ago against content hash 889518f985ca, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

parser-test-best-practices scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/rules/parser-test-best-practices.mdc · 35 lines

What it actually says

Parser Test Best Practices

AST and Parser Structure

  • Use barrel files (like ast_nodes.dart) to export related AST node types
  • Avoid circular dependencies in the AST node hierarchy
  • Use interfaces or abstract base classes for common node functionality
  • Create focused parser components with explicit interfaces

Error Reporting

  • Always use the correct error reporter method for the context
  • Use reportStandardError(message, offset) instead of reportError(message)
  • Include source position information for better error diagnostics
  • Categorize errors by severity and type when appropriate

Mock Implementations

  • Create simplified mock implementations that match interfaces exactly
  • Provide factory methods for common test fixtures
  • Separate parsing logic testing from AST construction
  • Ensure return types match the interface exactly (e.g., Model addElement returns Model, not void)

Test Assertions

  • Use flexible matchers for counts (greaterThanOrEqualTo instead of exact equality)
  • Use predicate-based element presence checks when appropriate
  • Create stub implementations for complex test cases to allow test suite to run
  • Test parser components independently before integration
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 35 lines · 249 tokens per session scan A 889518f985ca

Subscribe to this mod's changes

parser-test-best-practices is a cursor rule published in the GitHub repository Consiliency/Flutter-Structurizr (7 stars, last pushed 1mo ago), licensed MIT. It adds 249 tokens to every session, about $0.0012 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.