A TDD demo

This demo is created for demonstrating how to use TDD to implement a long-running task module in a spring-based web system based on database.

In this demo, we'll see:

• How does TDD help to finish our design.
• How does TDD help to create just-right components and APIs.
• How does TDD help to encourage us to use more domain language in our code.
• How does TDD provide security fence to give us confidence of our code.
• How does TDD help us fix potential bugs in code.

Basic analysis and design

• Start a background thread to handle tasks
• Use scheduling infrastructure provided by spring to trigger task periodically
• Use database transaction and version to handle multi-processes case
• Should clean zombie tasks and restart it automatically

Tests covered

Case 1: should run tasks

• Register task handler in consumer
• Add task to queue
• Task should be saved to database
• Consumer should fetch new tasks and run it
• The task should be handled after a while

Case 2: consumer should be waked up periodically

• Start one consumer
• Wait for a period to see if any logs printed to show that the consumer is fetching new tasks from the queue

Case 3: consumer should be waked up immediately if there is a new task added

• Start one consumer
• Wait until the consumer found non tasks and change to sleeping status
• Add a task to the queue
• Check if the consumer is wake up immediately to handle the new task

Case 4: zombie tasks should be cleaned and restart in other consumer

• Start one consumer
• Add 1 long-running task
• After the task added to the queue, kill the consumer process
• Start another consumer
• Wait until the other consumer to clean zombie tasks and pick up the cleaned task

Case 5: raise exception and fail task when no task handler registered for some task type

• Start one consumer
• Add 1 task with no handler registered
• Check to see if the task failed after a while.