MPG Calculation Service With TDD: A Backend Guide

by Alex Johnson 50 views

In this comprehensive guide, we will delve into the process of implementing a Miles Per Gallon (MPG) calculation service using Test-Driven Development (TDD). This is a crucial aspect of any automotive application, providing users with valuable insights into their vehicle's fuel efficiency. We'll explore the requirements, acceptance criteria, implementation notes, and dependencies involved in building a robust and reliable MPG calculation service.

Understanding the Requirements

Before we dive into the implementation, let's first understand the requirements for our MPG calculation service. The core of our service will be the FillupService class, which will contain the logic for calculating MPG. The most important part of this class is the calculateMPG() method, which will adhere to the specifications outlined in PRD Section 5. This section details the different scenarios for MPG calculation, which we will cover in detail below.

Service Layer: Building the Foundation

At the heart of our MPG calculation service lies the FillupService class. This class will encapsulate the core logic for calculating MPG based on fill-up data. The primary method within this class is calculateMPG(), which will take into account various factors such as odometer readings and fuel volume to determine the vehicle's fuel efficiency.

The calculateMPG() method is the cornerstone of our service. It will implement the MPG calculation logic based on the following formula: (current_odometer - previous_odometer) / fuel_volume. This formula represents the fundamental calculation for determining miles per gallon, where the difference in odometer readings is divided by the amount of fuel used.

Test Coverage: Ensuring Reliability through TDD

To ensure the reliability and accuracy of our MPG calculation service, we will adopt a Test-Driven Development (TDD) approach. This means that we will write tests before we write any code. This process will help us define the expected behavior of our service and ensure that it meets the requirements.

Specifically, we must test all three MPG calculation cases outlined in PRD.md Section 5. These cases cover various scenarios that can occur during fill-ups, including normal fill-ups, partial fill-ups, and missed fill-ups. By thoroughly testing each of these scenarios, we can ensure that our service functions correctly under a wide range of conditions.

  1. Normal Fill-up: In this scenario, the previous fill-up was a full tank (is_partial = false), and the current fill-up is also a full tank. The MPG is calculated using the standard formula: (current_odometer - previous_odometer) / fuel_volume. This is the most common scenario, and our service must accurately calculate MPG in this case.

  2. Partial Fill-up: When the current fill-up is partial (is_partial = true), we skip the MPG calculation and return null or N/A. This is because a partial fill-up does not provide enough information to accurately calculate MPG. However, we must preserve the chain for the next full fill-up, so that we can calculate MPG when a full fill-up occurs.

  3. Missed Fill-up: If the user sets is_missed = true on a previous fill-up, we break the MPG calculation chain. This means that we cannot calculate MPG for the current fill-up. This scenario is important to handle because it can occur when a user forgets to record a fill-up, which can disrupt the MPG calculation.

Acceptance Criteria: Defining Success

To ensure that our MPG calculation service meets the required standards, we have established a set of acceptance criteria. These criteria serve as a checklist to verify that the service functions correctly and adheres to best practices.

  • FillupServiceTest Class: We will create a FillupServiceTest class that contains all three test cases for MPG calculation. This class will serve as the foundation for our TDD process, allowing us to define the expected behavior of our service before we write any code.
  • Initial Test Failure (RED Phase): Before implementing the FillupService, all tests must initially fail. This is a crucial step in the TDD process, as it confirms that our tests are correctly set up and that they accurately reflect the requirements of the service.
  • Passing Tests After Implementation (GREEN Phase): Once we implement the FillupService, all tests must pass. This indicates that our service is functioning correctly and meets the specified requirements. Achieving the GREEN phase is the primary goal of the TDD process.
  • Code Coverage ≥ 80%: We will ensure that our service layer has a code coverage of at least 80%. This means that 80% of the code in our service layer is covered by tests. High code coverage is essential for ensuring the reliability and maintainability of our service.
  • make check-coverage Passes: We will use a tool like make check-coverage to verify that our code coverage meets the required threshold. This tool will automatically analyze our code and tests to determine the code coverage percentage.

Implementation Notes: Guiding Principles

To ensure a smooth and efficient implementation process, we have outlined a set of implementation notes. These notes provide guidance on best practices and considerations to keep in mind while developing the MPG calculation service.

  • TDD Approach: This is a TDD task, so it's crucial to write failing tests FIRST. This approach will guide the development process and ensure that the service meets the requirements.
  • PRD.md Reference: Refer to PRD.md Section 5 for the data model and flags. This document provides essential information about the data structures and flags used in the MPG calculation service.
  • Execution Plan: Refer to PRD.md Section 11 for the execution plan. This section outlines the steps involved in implementing the service and can help guide the development process.

Dependencies: Building on a Solid Foundation

Our MPG calculation service depends on the completion of other tasks. Specifically, it requires #5 (Database schema) to be completed first. This dependency ensures that the necessary database tables and structures are in place before we begin implementing the service.

This service also blocks the REST API implementation. This means that the REST API cannot be implemented until the MPG calculation service is complete. This dependency ensures that the core business logic is in place before the API is built.

Definition of Done: Marking Completion

To clearly define when the MPG calculation service is complete, we have established a set of criteria that must be met. These criteria serve as a final checklist to ensure that all aspects of the service are implemented and functioning correctly.

  • Passing Tests: All three MPG calculation scenarios must have passing tests. This confirms that the service functions correctly under various conditions.
  • Code Coverage: The service layer must have 80%+ coverage. This ensures that a significant portion of the code is covered by tests, increasing the reliability of the service.
  • Spring Best Practices: The code must follow Spring best practices. This ensures that the code is well-structured, maintainable, and adheres to industry standards.
  • Documentation/JavaDoc: Documentation and JavaDoc must be added. This provides clarity and context for the code, making it easier to understand and maintain.

Step-by-Step Implementation Guide

Now, let's walk through the step-by-step process of implementing the MPG calculation service using TDD.

Step 1: Setting up the Test Environment

First, we need to set up the test environment. This involves creating the FillupServiceTest class and configuring the necessary dependencies for testing.

  1. Create the FillupServiceTest class in the appropriate test directory.
  2. Add necessary dependencies, such as JUnit and Mockito, to the project's build configuration.
  3. Configure the test environment to run in a consistent and isolated manner.

Step 2: Writing Failing Tests (RED Phase)

Next, we will write the failing tests for each of the three MPG calculation scenarios.

  1. Create test methods for each scenario: Normal Fill-up, Partial Fill-up, and Missed Fill-up.
  2. Write assertions that reflect the expected behavior for each scenario.
  3. Run the tests and verify that they all fail (RED phase).

Step 3: Implementing the FillupService (GREEN Phase)

Now, we will implement the FillupService to make the tests pass.

  1. Create the FillupService class and the calculateMPG() method.
  2. Implement the MPG calculation logic based on the requirements and the test cases.
  3. Run the tests and verify that they all pass (GREEN phase).

Step 4: Refactoring and Code Coverage

After the tests pass, we will refactor the code to improve its structure and readability.

  1. Refactor the code to adhere to Spring best practices.
  2. Ensure that the code is well-documented and easy to understand.
  3. Check the code coverage and ensure that it is at least 80%.

Step 5: Final Verification

Finally, we will perform a final verification to ensure that the service is complete and meets all the requirements.

  1. Run all tests one last time to ensure that they still pass.
  2. Verify that the code coverage is still at least 80%.
  3. Ensure that the code is well-documented and follows Spring best practices.

Conclusion

Implementing an MPG calculation service using TDD is a systematic and effective way to ensure the reliability and accuracy of the service. By writing tests first, we can define the expected behavior of the service and ensure that it meets the requirements. This approach also helps us to catch errors early in the development process, which can save time and effort in the long run. By following the steps outlined in this guide, you can build a robust and reliable MPG calculation service that meets the needs of your application.

For more information on Test-Driven Development, you can visit the TDD entry on Wikipedia.