backend-api-test

name	backend-api-test
description	Guidelines for writing backend API tests using pytest and FastAPI TestClient. Use this skill when writing or modifying tests in tests/backend directory.

Backend API Testing Guidelines

This skill provides comprehensive guidelines for writing backend API tests for the Factory Inventory Management System. Follow these patterns to ensure consistent, thorough test coverage.

Directory Structure

All backend tests must be placed in tests/backend/:

tests/backend/
├── conftest.py           # Shared fixtures and test client setup
├── test_inventory.py     # Inventory endpoint tests
├── test_orders.py        # Orders endpoint tests
├── test_dashboard.py     # Dashboard endpoint tests
└── test_misc_endpoints.py # Other endpoint tests

File Organization

1. File Naming

• Use test_<feature>.py format (e.g., test_inventory.py, test_orders.py)
• Group related endpoints in the same file
• Create new files for distinct API feature areas

2. Test Class Structure

Organize tests within a class using descriptive names:

"""
Tests for <feature> API endpoints.
"""
import pytest


class Test<Feature>Endpoints:
    """Test suite for <feature>-related endpoints."""

    def test_get_all_<resources>(self, client):
        """Test getting all <resources>."""
        # Test implementation

Core Testing Patterns

1. Basic Endpoint Tests

Always test the happy path first:

def test_get_all_orders(self, client):
    """Test getting all orders."""
    response = client.get("/api/orders")
    assert response.status_code == 200

    data = response.json()
    assert isinstance(data, list)
    assert len(data) > 0

    # Verify structure of first item
    first_order = data[0]
    assert "id" in first_order
    assert "order_number" in first_order
    # ... other required fields

2. Filter Testing

Test each query parameter filter individually and in combination:

def test_get_orders_by_warehouse(self, client):
    """Test filtering orders by warehouse."""
    response = client.get("/api/orders?warehouse=Tokyo")
    assert response.status_code == 200

    data = response.json()
    assert isinstance(data, list)

    # Verify all results match the filter
    for order in data:
        assert order["warehouse"] == "Tokyo"

def test_get_orders_multiple_filters(self, client):
    """Test filtering orders with multiple filters."""
    response = client.get(
        "/api/orders?warehouse=San Francisco&category=Power Supplies&status=Delivered"
    )
    assert response.status_code == 200

    data = response.json()

    # Verify all results match ALL filters
    for order in data:
        assert order["warehouse"] == "San Francisco"
        assert order["category"].lower() == "power supplies"
        assert order["status"].lower() == "delivered"

Common filters to test:

• warehouse - Filter by warehouse location
• category - Filter by product category
• status - Filter by order status (orders only)
• month - Filter by month in format YYYY-MM or quarter Q1-2025

3. Single Resource Tests

Test fetching individual resources by ID:

def test_get_order_by_id(self, client):
    """Test getting a specific order by ID."""
    # First get all orders to find a valid ID
    response = client.get("/api/orders")
    all_orders = response.json()
    assert len(all_orders) > 0

    first_order_id = all_orders[0]["id"]

    # Now get that specific order
    response = client.get(f"/api/orders/{first_order_id}")
    assert response.status_code == 200

    order = response.json()
    assert order["id"] == first_order_id

def test_get_nonexistent_order(self, client):
    """Test getting an order that doesn't exist."""
    response = client.get("/api/orders/nonexistent-order-999")
    assert response.status_code == 404

    data = response.json()
    assert "detail" in data
    assert "not found" in data["detail"].lower()

4. Data Structure Validation

Verify the response structure matches the API contract:

def test_order_items_structure(self, client):
    """Test that order items have proper structure."""
    response = client.get("/api/orders")
    data = response.json()

    for order in data:
        assert "items" in order
        assert isinstance(order["items"], list)

        for item in order["items"]:
            assert "sku" in item
            assert "name" in item
            assert "quantity" in item
            assert "unit_price" in item
            assert isinstance(item["quantity"], int)
            assert isinstance(item["unit_price"], (int, float))

5. Data Type Validation

Ensure numeric fields have correct types and valid ranges:

def test_inventory_quantity_types(self, client):
    """Test that quantity fields are proper numeric types."""
    response = client.get("/api/inventory")
    data = response.json()

    for item in data:
        assert isinstance(item["quantity_on_hand"], int)
        assert isinstance(item["reorder_point"], int)
        assert isinstance(item["unit_cost"], (int, float))
        assert item["quantity_on_hand"] >= 0
        assert item["reorder_point"] >= 0
        assert item["unit_cost"] >= 0

6. Business Logic Validation

Test calculated values and business rules:

def test_order_total_value_calculation(self, client):
    """Test that order total values are reasonable."""
    response = client.get("/api/orders")
    data = response.json()

    for order in data:
        assert "total_value" in order
        assert isinstance(order["total_value"], (int, float))
        assert order["total_value"] > 0

        # Verify total makes sense based on items
        calculated_total = sum(
            item["quantity"] * item["unit_price"]
            for item in order["items"]
        )
        # Allow small floating point differences
        assert abs(order["total_value"] - calculated_total) < 0.01

7. Enum/Status Value Validation

Verify constrained fields have valid values:

def test_order_status_values(self, client):
    """Test that orders have valid status values."""
    response = client.get("/api/orders")
    data = response.json()

    valid_statuses = ["delivered", "shipped", "processing", "backordered"]

    for order in data:
        assert order["status"].lower() in valid_statuses

8. Date Format Validation

Verify date fields are properly formatted:

def test_order_dates_format(self, client):
    """Test that order dates are in proper format."""
    response = client.get("/api/orders")
    data = response.json()

    for order in data:
        assert "order_date" in order
        assert "expected_delivery" in order
        # Date should contain year, month pattern (ISO format)
        assert "2025-" in order["order_date"]
        assert "-" in order["expected_delivery"]
        assert "T" in order["expected_delivery"]  # Has time component

9. Cross-Endpoint Validation

Test that aggregated endpoints match raw data:

def test_dashboard_pending_orders_calculation(self, client):
    """Test that pending orders are calculated correctly."""
    # Get all orders
    orders_response = client.get("/api/orders")
    all_orders = orders_response.json()

    # Count processing and backordered orders
    pending_count = sum(
        1 for order in all_orders
        if order["status"].lower() in ["processing", "backordered"]
    )

    # Get dashboard summary
    dashboard_response = client.get("/api/dashboard/summary")
    dashboard_data = dashboard_response.json()

    assert dashboard_data["pending_orders"] == pending_count

Using Fixtures

Available Fixtures (from conftest.py)

1. client - FastAPI TestClient instance (required for all tests)
2. sample_inventory_item - Example inventory item structure
3. sample_order - Example order structure

Using the Client Fixture

def test_example(self, client):
    """Every test method needs the client fixture."""
    response = client.get("/api/endpoint")
    assert response.status_code == 200

Creating New Fixtures

Add shared fixtures to conftest.py:

@pytest.fixture
def sample_warehouse_data():
    """Sample warehouse data for testing."""
    return {
        "name": "San Francisco",
        "location": "CA",
        # ... other fields
    }

Test Naming Conventions

Use descriptive names that clearly indicate what is being tested:

• test_get_all_<resources> - Get all items without filters
• test_get_<resource>_by_<filter> - Single filter tests
• test_get_<resource>_multiple_filters - Combined filter tests
• test_get_<resource>_by_id - Single item retrieval
• test_get_nonexistent_<resource> - 404 handling
• test_<resource>_<field>_structure - Data structure validation
• test_<resource>_<field>_types - Data type validation
• test_<resource>_<calculation>_calculation - Business logic

Common Assertions

Status Codes

assert response.status_code == 200  # Success
assert response.status_code == 404  # Not found
assert response.status_code == 422  # Validation error

Response Types

data = response.json()
assert isinstance(data, list)    # Array response
assert isinstance(data, dict)    # Object response
assert len(data) > 0             # Has data

Field Presence

assert "field_name" in data
assert "detail" in error_response  # Error messages

String Comparisons (Case-Insensitive)

assert order["status"].lower() == "delivered"
assert item["category"].lower() == "power supplies"

Floating Point Comparisons

# Allow small differences for float calculations
assert abs(calculated - expected) < 0.01

API Endpoint Reference

Inventory Endpoints

• GET /api/inventory - All inventory items
  • Filters: warehouse, category
• GET /api/inventory/{id} - Single inventory item

Orders Endpoints

• GET /api/orders - All orders
  • Filters: warehouse, category, status, month
• GET /api/orders/{id} - Single order

Dashboard Endpoints

• GET /api/dashboard/summary - Dashboard summary
  • Filters: warehouse, category, status, month

Other Endpoints

• GET /api/demand - Demand forecast (no filters)
• GET /api/backlog - Backlog items (no filters)
• GET /api/spending/* - Spending data endpoints

Common Values for Testing

Warehouses

• San Francisco
• London
• Tokyo

Categories

• Circuit Boards
• Sensors
• Power Supplies
• Connectors
• Mechanical Components

Order Statuses

• Delivered
• Shipped
• Processing
• Backordered

Date Formats

• Single month: 2025-01, 2025-02, etc.
• Quarter: Q1-2025, Q2-2025, etc.
• All: all

Best Practices

1. Test one thing per test - Each test should verify a single behavior
2. Use descriptive assertions - Clear error messages help debugging
3. Test edge cases - Empty results, nonexistent IDs, invalid filters
4. Verify data integrity - Check types, ranges, and calculated values
5. Test filters independently - Then test combinations
6. Use case-insensitive comparisons - For string fields like status/category
7. Allow floating point tolerance - Use abs(a - b) < 0.01 for money calculations
8. Test error responses - Verify proper 404 handling
9. Validate complete structure - Check all required fields are present
10. Cross-validate endpoints - Dashboard should match raw data

Running Tests

# Run all backend tests
pytest tests/backend/

# Run specific test file
pytest tests/backend/test_orders.py

# Run specific test class
pytest tests/backend/test_orders.py::TestOrdersEndpoints

# Run specific test method
pytest tests/backend/test_orders.py::TestOrdersEndpoints::test_get_all_orders

# Run with verbose output
pytest tests/backend/ -v

# Run with coverage
pytest tests/backend/ --cov=server

Example: Complete Test File Template

"""
Tests for <feature> API endpoints.
"""
import pytest


class Test<Feature>Endpoints:
    """Test suite for <feature>-related endpoints."""

    def test_get_all_<resources>(self, client):
        """Test getting all <resources>."""
        response = client.get("/api/<resources>")
        assert response.status_code == 200

        data = response.json()
        assert isinstance(data, list)
        assert len(data) > 0

        # Verify structure
        first_item = data[0]
        assert "id" in first_item
        # Add other required fields

    def test_get_<resource>_by_filter(self, client):
        """Test filtering <resources> by <filter>."""
        response = client.get("/api/<resources>?<filter>=<value>")
        assert response.status_code == 200

        data = response.json()

        # Verify filter applied correctly
        for item in data:
            assert item["<filter>"] == "<value>"

    def test_get_<resource>_by_id(self, client):
        """Test getting a specific <resource> by ID."""
        # Get valid ID first
        response = client.get("/api/<resources>")
        all_items = response.json()
        item_id = all_items[0]["id"]

        # Get specific item
        response = client.get(f"/api/<resources>/{item_id}")
        assert response.status_code == 200

        item = response.json()
        assert item["id"] == item_id

    def test_get_nonexistent_<resource>(self, client):
        """Test getting a <resource> that doesn't exist."""
        response = client.get("/api/<resources>/nonexistent-999")
        assert response.status_code == 404

        data = response.json()
        assert "detail" in data
        assert "not found" in data["detail"].lower()

Key Reminders

• Always use the client fixture - It's the TestClient for making API calls
• Test filters thoroughly - Individual filters and combinations
• Validate response structure - Check all required fields exist
• Use lowercase for string comparisons - Categories and statuses vary in case
• Test both success and error paths - 200 and 404 responses
• Verify data types - Use isinstance() for proper type checking
• Test business logic - Calculations, aggregations, and derived values
• Keep tests independent - Each test should work in isolation