149 lines
3.1 KiB
Markdown
149 lines
3.1 KiB
Markdown
---
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name: test-writer
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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.
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---
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# Test Writer Skill
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## Overview
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This skill provides guidelines for writing clean, maintainable Elixir/Phoenix tests following best practices.
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## Core Principles
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### 1. DRY Tests
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Avoid duplication by creating focused helper functions:
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**Bad:**
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```elixir
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test "GET /users returns index", %{conn: conn} do
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conn = get(conn, "/users")
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body = html_response(conn, 200)
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assert body =~ "Users"
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end
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test "GET /users/:id returns show", %{conn: conn} do
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conn = get(conn, "/users/1")
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body = html_response(conn, 200)
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assert body =~ "User"
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end
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```
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**Good:**
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```elixir
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defp goto_users_page(conn, suffix \\ ""), do: get(conn, "/users" <> suffix)
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test "GET /users returns index", %{conn: conn} do
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conn = goto_users_page(conn)
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assert html_response(conn, 200) =~ "Users"
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end
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test "GET /users/:id returns show", %{conn: conn} do
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conn = goto_users_page(conn, "/1")
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assert html_response(conn, 200) =~ "User"
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end
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```
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### 2. Separate Helpers for Different Assertion Patterns
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Don't use conditionals in helpers to handle different cases:
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**Bad:**
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```elixir
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defp goto_users_page(conn, suffix \\ "", check_title \\ true) do
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path = "/users" <> suffix
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conn = get(conn, path)
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body = html_response(conn, 200)
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if check_title, do: assert body =~ "Users"
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assert body =~ "AppLayout"
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body
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end
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```
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**Good:**
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```elixir
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defp goto_users_page(conn, suffix \\ "") do
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path = "/users" <> suffix
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conn = get(conn, path)
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body = html_response(conn, 200)
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assert body =~ "Users"
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assert body =~ "AppLayout"
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body
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end
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defp goto_user_page(conn, suffix) do
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path = "/users" <> suffix
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conn = get(conn, path)
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body = html_response(conn, 200)
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assert body =~ "AppLayout"
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body
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end
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```
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## Test Structure
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### Context Block
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```elixir
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describe "resource name" do
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# Shared setup in context if needed
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# test "scenario" do ...
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end
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```
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### Value Aliasing
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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.
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```elixir
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test "GET /users returns index", %{conn: conn} do
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# don't reassign
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response = get(conn, "/users")
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# ...
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end
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```
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## Common Patterns
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### HTML Pages with Layout
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```elixir
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defp goto_resource_page(conn, suffix \\ ""), do: ...
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# Asserts common layout elements and page-specific content
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```
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### API Endpoints
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```elixir
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test "GET /api/resource returns JSON", %{conn: conn} do
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conn = conn |> put_req_header("accept", "application/json")
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conn = get(conn, "/api/resource")
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response = json_response(conn, 200)
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# Assert structure
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end
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```
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### Error Handling
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```elixir
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test "returns 404 for nonexistent", %{conn: conn} do
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assert html_response(get(conn, "/nonexistent"), 404)
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end
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```
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## Running Tests
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### One focused test file
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```bash
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cd /path/to/app
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mix test test/path/to_test.exs
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```
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### all tests
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```bash
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make test
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```
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