test writer skill

Focuses on integration tests, but might be more reusable

.pi/skills/test-writer/SKILL.md

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+---
+name: test-writer
+description: Writes tests following Elixir/Phoenix best practices. Ensures DRY tests with proper helper functions, no duplicated setup code, and correct parameter defaults. Use when writing or modifying tests.
+---
+
+# Test Writer Skill
+
+## Overview
+
+This skill provides guidelines for writing clean, maintainable Elixir/Phoenix tests following best practices.
+
+## Core Principles
+
+### 1. DRY Tests
+
+Avoid duplication by creating focused helper functions:
+
+**Bad:**
+```elixir
+test "GET /users returns index", %{conn: conn} do
+  conn = get(conn, "/users")
+  body = html_response(conn, 200)
+  assert body =~ "Users"
+end
+
+test "GET /users/:id returns show", %{conn: conn} do
+  conn = get(conn, "/users/1")
+  body = html_response(conn, 200)
+  assert body =~ "User"
+end
+```
+
+**Good:**
+```elixir
+defp goto_users_page(conn, suffix \\ ""), do: get(conn, "/users" <> suffix)
+
+test "GET /users returns index", %{conn: conn} do
+  conn = goto_users_page(conn)
+  assert html_response(conn, 200) =~ "Users"
+end
+
+test "GET /users/:id returns show", %{conn: conn} do
+  conn = goto_users_page(conn, "/1")
+  assert html_response(conn, 200) =~ "User"
+end
+```
+
+
+### 2. Separate Helpers for Different Assertion Patterns
+
+Don't use conditionals in helpers to handle different cases:
+
+**Bad:**
+```elixir
+defp goto_users_page(conn, suffix \\ "", check_title \\ true) do
+  path = "/users" <> suffix
+  conn = get(conn, path)
+  body = html_response(conn, 200)
+  if check_title, do: assert body =~ "Users"
+  assert body =~ "AppLayout"
+  body
+end
+```
+
+**Good:**
+```elixir
+defp goto_users_page(conn, suffix \\ "") do
+  path = "/users" <> suffix
+  conn = get(conn, path)
+  body = html_response(conn, 200)
+  assert body =~ "Users"
+  assert body =~ "AppLayout"
+  body
+end
+
+defp goto_user_page(conn, suffix) do
+  path = "/users" <> suffix
+  conn = get(conn, path)
+  body = html_response(conn, 200)
+  assert body =~ "AppLayout"
+  body
+end
+```
+
+## Test Structure
+
+### Context Block
+
+```elixir
+describe "resource name" do
+  # Shared setup in context if needed
+  # test "scenario" do ...
+end
+```
+
+### Value Aliasing
+
+Never reuse value names. Elixir is immutable, but value aliasing is confusing. Use unique, meaningful names for the left hand side of assignments. Or use pipes `|>` to eliminate the need for naming.
+
+```elixir
+test "GET /users returns index", %{conn: conn} do
+  # don't reassign
+  response = get(conn, "/users")
+  # ...
+end
+```
+
+## Common Patterns
+
+### HTML Pages with Layout
+
+```elixir
+defp goto_resource_page(conn, suffix \\ ""), do: ...
+# Asserts common layout elements and page-specific content
+```
+
+### API Endpoints
+
+```elixir
+test "GET /api/resource returns JSON", %{conn: conn} do
+  conn = conn |> put_req_header("accept", "application/json")
+  conn = get(conn, "/api/resource")
+  response = json_response(conn, 200)
+  # Assert structure
+end
+```
+
+### Error Handling
+
+```elixir
+test "returns 404 for nonexistent", %{conn: conn} do
+  assert html_response(get(conn, "/nonexistent"), 404)
+end
+```
+
+## Running Tests
+
+### One focused test file
+
+```bash
+cd /path/to/app
+mix test test/path/to_test.exs
+```
+
+### all tests
+```bash
+make test
+```