docs: 📝 add 202-contract-testing instructions

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: yjaaidi

docs/instructions/202-contract-testing.md

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+---
+sidebar_label: 202. Contract Testing
+---
+
+# Contract Testing
+
+## Setup
+
+```sh
+pnpm cook start 202-contract-testing
+```
+
+To make sure that the fake and the real implementation behave the same way, you will implement a **contract test**: a shared suite of expectations that will run against **every** implementation. In this project, `verifyRecipeRepositoryContract` is already wired up for:
+
+- `RecipeRepositoryFake` in `recipe-repository.fake.spec.ts` (in-memory, fast)
+- the real HTTP `RecipeRepository` in `recipe-repository.wide.spec.ts` (slow, hits the network)
+
+You must **implement the contract**.
+
+## 🎯 Goal #1: `searchRecipes()` returns all recipes
+
+When called with no filter, the repository should return recipes — including at least one named **Burger** (present in both the fake seed data and the remote API).
+
+### 📝 Steps
+
+#### 1. Run tests in watch mode.
+
+```sh
+pnpm test
+```
+
+#### 2. Go to `src/app/recipe/recipe-repository.contract.ts`.
+
+#### 3. Implement the **returns all recipes** test.
+
+- Create the recipe repository using the `createRecipeRepositoryFake` factory function.
+- Call `searchRecipes()` with no arguments.
+- Assert the result **contains** a recipe whose `name` is `Burger` (See [Partial object matching](#-partial-object-matching)).
+
+#### 4. Turn on the test by replacing `it.todo` with `it`.
+
+#### 5. Make sure the test passes for both the fake and the real implementation.
+
+## 🎯 Goal #2: `searchRecipes` filters by keywords
+
+Calling `searchRecipes({ keywords: 'burg' })` should return only recipes whose names match that filter — no unrelated recipes in the result.
+
+### 📝 Steps
+
+#### 1. Go to `src/app/recipe/recipe-repository.contract.ts`.
+
+#### 2. Implement the **filters recipes containg "burg" keywords** test.
+
+- Call `searchRecipes({ keywords: 'burg' })`.
+- Split results into recipes whose `name` includes `Burger` and recipes that do not.
+- Assert there is **at least one** burger recipe, and **no** other recipes.
+
+#### 3. Replace `it.todo` with `it`.
+
+#### 4. Make sure the test passes for both the fake and the real implementation.
+
+## 🎯 Goal #3: No match returns an empty array
+
+### 📝 Steps
+
+#### 1. Go to `src/app/recipe/recipe-repository.contract.ts`.
+
+#### 2. Implement the **returns an empty array when no recipes are found** test.
+
+- Call `searchRecipes` with keywords that cannot match any seeded or API recipe (e.g. `pizza with salmon and pineapple`).
+- Assert the result has length `0`.
+
+#### 3. Replace `it.todo` with `it`.
+
+#### 4. Make sure the test passes for both the fake and the real implementation.
+
+## 📖 Appendices
+
+### 🎁 Partial object matching
+
+Use `toContainEqual` with `expect.objectContaining` when you only care about a subset of fields:
+
+```ts
+expect(recipes).toContainEqual(expect.objectContaining({ name: 'Burger' }));
+```
+
+This avoids brittle full-object equality when recipes carry ids, ingredients, etc.