Test-First Development Skill

Test-First Development (TDD) ensures that code is written to satisfy specific, predefined requirements, leading to higher quality and better design.

TDD Workflow

Red

Write a failing test for a small piece of functionality.

Green

Write the minimum amount of code required to make the test pass.

Refactor

Clean up the code while ensuring the tests remain green.

Test Design Principles

1. Comprehensive Coverage

Normal Cases

Test the expected "happy path" behavior.

Boundary Values

Test inputs at the edges of valid ranges (e.g., 0, max_int, empty strings).

Edge Cases

Test unusual or extreme conditions (e.g., network timeout, disk full, null values).

Error Handling

Verify that the system fails gracefully and returns appropriate error messages.

2. Structure (Arrange-Act-Assert)

Follow the AAA pattern for clear and maintainable tests:

Arrange

Set up the necessary preconditions and inputs.

Act

Execute the function or method being tested.

Assert

Verify that the outcome matches the expectation.

Best Practices

One Assertion per Test

Aim to test a single concept per test case.

Descriptive Naming

Name tests clearly (e.g.,

test_should_reject_invalid_api_key

).

Independence

Ensure tests do not depend on each other or on a specific execution order.

Fast Execution

Keep unit tests fast to encourage frequent execution.