tdd-lab.md

Objective

Students will extend their existing Employee Management API by using the TDD cycle:

1. Write a test
2. Run the test
3. See it fail
4. Write the code
5. Run the test again
6. Refactor if needed

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Starting Point

Students already have:

• GET /employees
• POST /employees
• GET /employees/{id}
• PUT /employees/{id}
• DELETE /employees/{id}

They also have a simple in-memory or MongoDB-backed employee app.

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TDD Rule for This Lab

For every new feature:

• Step 1: Write test first
• Step 2: Run test and confirm failure
• Step 3: Implement feature
• Step 4: Run tests again
• Step 5: Clean up code if needed

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Features to Add

Feature 1: Filter Employees by Department

API

GET /employees?department=IT

Expected Behavior

• Return only employees from the given department
• If no employees match, return an empty list

Test Ideas

• department exists
• department does not exist
• multiple employees in same department

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Feature 2: Search Employees by Name

API

GET /employees?name=John

Expected Behavior

• Return matching employees
• Partial match is a bonus
• Case-insensitive match is a bonus

Test Ideas

• exact name match
• no match found
• optional: partial name match

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Feature 3: Prevent Duplicate Email

Rule

Two employees cannot have the same email.

Expected Behavior

• If duplicate email is submitted, return error
• Suggested status code: 400

Test Ideas

• create first employee with email
• create second employee with same email
• verify second request fails

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Feature 4: Validate Required Fields

Rule

Employee must have:

• name
• email
• role
• department

Expected Behavior

• Missing field returns 400 or validation error

Test Ideas

• missing name
• missing email
• missing role
• missing department

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Feature 5: Employee Summary Endpoint

API

GET /employees/summary

Expected Response Example

{
  "total_employees": 5,
  "departments": ["IT", "HR", "Finance"]
}

Test Ideas

• returns correct total count
• returns unique department list

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Minimum Required Work

Each student or team must complete at least:

• 3 new features
• test cases for each feature
• proof that tests failed before code was added
• proof that tests passed after implementation

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Suggested Test File

test_main.py

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Recommended Tools

• pytest
• fastapi.testclient.TestClient

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Example TDD Workflow

Example: Duplicate Email Check

Step 1 — Write Test

def test_create_employee_duplicate_email():
    ...

Step 2 — Run Test

• test fails

Step 3 — Add Logic

• check whether email already exists

Step 4 — Run Test Again

• test passes

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Deliverables

Students must submit:

1. Updated application code

2. test_main.py

3. Screenshot or terminal output showing:

   • failing tests first
   • passing tests later

4. Short note answering:

   • Which features did you add?
   • Which test did you write first?
   • What bug or failure did the test catch?

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Student Instructions

Use AI, but follow this rule:

Do not ask AI to only write the feature. Ask AI to write the test first.

Example Prompt

Write pytest test cases first for my FastAPI employee app.

I want to add:
1. filter by department
2. duplicate email validation
3. employee summary endpoint

Keep tests beginner-friendly.
Explain what each test is checking.
Do not write the feature code yet.

Then after tests fail:

Now implement only the code needed to make these tests pass.
Keep the code simple and readable.
Explain what changed.