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David Chibueze Ndubuisi
David Chibueze Ndubuisi

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Automate Unit Testing with Cover-Agent: The Latest Innovation from CodiumAI

Cover Agent Prompt

Have you ever felt like writing unit tests is the coding equivalent of washing the dishes? Have you thought about how tedious, repetitive, and never-ending it can be? Even though unit tests are crucial for developing reliable and robust software, the process can be a real drain on developer productivity. Surely, there must be a more efficient way to handle this.

That's where CodiumAI comes in. Dedicated to transforming the developer experience with advanced AI tools, their latest innovation, an open-source tool called Cover-Agent, could be the breakthrough you've been waiting for. Picture an AI assistant that analyzes your code, understands its purpose, and even suggests new tests to ensure its quality. It sounds like science fiction, but Cover-Agent is making that vision a reality right now.

Before we explore this amazing tool, let's take a step back to understand why unit tests are so important. They are essential for ensuring code quality, and catching errors before they become real-world problems. They act as code monitors, identifying potential bugs and ensuring your software functions correctly. However, you'd agree that writing these tests can be time-consuming and requires a solid understanding of your code. That's where Cover-Agent steps in. It automates test generation, allowing you to focus on the exciting, creative aspects of coding.

Ready to ditch the labor of manual testing? This article will provide an in-depth look at Cover-Agent, explaining how it works and its benefits, breaking down its components, and guiding you through installation and usage. With practical examples and clear instructions, you'll see how Cover-Agent can seamlessly fit into your workflow, boosting productivity and enhancing your codebase's reliability. Buckle up, because the future of unit testing is here, and it's powered by AI!

What is Cover-Agent?

Cover-Agent, developed by CodiumAI, is an innovative open-source tool that harnesses Generative AI to automate the writing of unit tests for software projects. It streamlines the testing process, offering comprehensive code coverage and eliminating the repetitive and time-consuming task of writing unit tests manually. With Cover-Agent, developers can focus more on building new features, boosting both productivity and code quality.

Key Features and Capabilities

  • Generative AI at its Core: Cover-Agent leverages cutting-edge Generative AI models to understand your code. It automatically generates unit tests based on your existing code, significantly reducing the time spent on manual test writing.
  • Multiple Programming Language Support: Whether you're coding in Python, Go, or other popular languages, Cover-Agent is designed to work seamlessly with your preferred environment.
  • Integration with Existing Workflows: Cover-Agent is built to integrate with your existing development process. You can use it as a standalone tool or integrate it into your CI/CD pipeline for a fully automated testing experience.
  • Flexibility and Customization: Cover-Agent offers various configuration options to tailor its test generation to your specific project needs. You can define desired code coverage goals, set the number of test iterations, and even specify certain files or functionalities to focus on.

These features will be better explained in the coming sections.

Components of Cover-Agent

Now that we understand Cover-Agent's purpose and potential, let's dive into the components:

Test Runner

The Test Runner is an important component of Cover-Agent, responsible for executing the test suite and generating code coverage reports. It ensures that the tests are run correctly and that the results are accurately captured, providing developers with a clear understanding of their code's coverage and reliability.

The Test Runner executes the specified command or script to run the tests within the codebase. For instance, when working with a Python project, you might run the following command:

cover-agent \
  --source-file-path "templated_tests/python_fastapi/" \
  --test-file-path "templated_tests/python_fastapi/" \
  --code-coverage-report-path "templated_tests/python_fastapi/coverage.xml" \
  --test-command "pytest --cov=. --cov-report=xml --cov-report=term" \
  --test-command-dir "templated_tests/python_fastapi" \
  --coverage-type "cobertura" \
  --desired-coverage 70 \
  --max-iterations 10
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In this example, the Test Runner executes the pytest command to run the tests and generate coverage reports in XML and terminal formats. The results are then collected and analyzed, highlighting which parts of the code are covered by the tests and identifying any gaps in coverage.

Coverage Parser

The Coverage Parser plays a vital role in validating that the tests generated by Cover-Agent effectively increase overall code coverage. It analyzes the coverage reports produced by the Test Runner to verify that new tests contribute to higher coverage percentages.

By parsing the coverage data, the Coverage Parser ensures that each new test adds value by covering previously untested code or by enhancing the thoroughness of existing tests. For example, after running the Test Runner, the Coverage Parser would check the coverage.xml file to ensure that the newly generated tests increase the overall coverage, aiming to reach the desired coverage goal set by the user (e.g., 70%).

Prompt Builder

The Prompt Builder is the mastermind behind developing the instructions for the LLM (Large Language Model) at the heart of Cover-Agent. Firstly, it gets into the codebase, analyzing functions, variables, and overall program logic, gathering all the necessary information about your code. Then, using the extracted information, the Prompt Builder constructs a clear and concise prompt for the LLM. This prompt tells the LLM what the code does and what kind of test scenarios it should generate.

AI Caller

The AI Caller is the interface between Cover-Agent and the Large Language Model (LLM). It sends the constructed prompts to the LLM and retrieves the generated tests. This interaction is central to the automated test generation process, leveraging the AI's capabilities to create high-quality tests.

For example, when the AI Caller sends a prompt describing a function in the file, the LLM generates a corresponding unit test in If the initial test does not achieve the desired coverage or fails to meet specific criteria, the AI Caller can iterate by refining the prompt and generating additional tests until the requirements are met. This iterative process ensures that the generated tests are both accurate and comprehensive, providing robust coverage for the codebase.

Installation and Setup

Setting up Cover-Agent is straightforward and involves a few key steps. Here's a comprehensive guide to get you started.


Before you begin, ensure you have the following requirements in place:

  • Python
  • Poetry


To use the AI capabilities of Cover-Agent, you need an API key from OpenAI. Follow these steps to obtain and set up your API key:

A. Obtain an API Key:

  • Sign up for an account at OpenAI's website.
  • Once logged in, go to the API section of your account to generate an API key.

B. Set the API Key in Your Environment Variables:

  • On Windows:

i. Open Command Prompt or PowerShell.
ii. Run the following command to set the environment variable:

setx OPENAI_API_KEY "your_openai_api_key_here"

iii. Restart your terminal or command prompt to apply the changes.

  • On macOS/Linux:\

i. Open a terminal window.
ii. Run the following command to set the environment variable:

export OPENAI_API_KEY="your_openai_api_key_here"
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iii. To make this change permanent, add the above line to your shell configuration file (~/.bashrc, ~/.zshrc, etc.) and source the file:

source ~/.bashrc  # or source ~/.zshrc
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Cover-Agent requires Python to be installed on your system. Here's how to check if Python is installed and how to install it if it’s not:

A. Check if Python is installed: Open a terminal or command prompt and run the following command:

python --version
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If Python is installed, you will see a version number. If not, proceed to install Python from the website


Poetry is used for managing Python package dependencies. Follow these steps to install Poetry:

A. Install Poetry:

  • Open a terminal or command prompt.
  • Run the following command to install Poetry:
curl -sSL | python3 -
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  • Follow any additional instructions provided by the installer.

B. Verify the Installation:

  • After installation, verify that Poetry is installed correctly by running:
poetry --version
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Standalone Runtime

Cover-Agent can be installed and run in two main ways: via a Python Pip package or as a standalone binary executable.

Installation via Python Pip Package

To install Cover-Agent directly from the GitHub repository using Pip, follow these steps:

  • Open a terminal or command prompt.
  • Run the following command:
pip install git+
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Running the Binary without a Python Environment

Cover-Agent GitHub Release Page

If you prefer not to install Python and its dependencies, you can run Cover-Agent as a standalone binary. Here’s how:

A. Download the Binary:

B. Run the Binary:

  • Open a terminal or command prompt in the directory where you downloaded the binary.
  • Run the binary directly. For example, on Linux or macOS:
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  • On Windows, run:
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Usage Instructions

Now that Cover-Agent is all set up on your system, let's put it to the test (literally)! Using Cover-Agent involves running commands in the terminal with various parameters to generate and validate unit tests. This section provides detailed instructions on how to use Cover-Agent, including command examples for different scenarios and an explanation of command parameters.

Detailed Command-Line Usage

To use Cover-Agent effectively, you need to run a command in the terminal with specific parameters. Below is the basic structure of the command and a detailed explanation of each parameter:

cover-agent \
  --source-file-path "<path_to_source_file>" \
  --test-file-path "<path_to_test_file>" \
  --code-coverage-report-path "<path_to_coverage_report>" \
  --test-command "<test_command_to_run>" \
  --test-command-dir "<directory_to_run_test_command>" \
  --coverage-type "<type_of_coverage_report>" \
  --desired-coverage <desired_coverage_between_0_and_100> \
  --max-iterations <max_number_of_llm_iterations>
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Explanation of Command Parameters
  • --source-file-path: This parameter specifies the path to the source code file for which you want to generate unit tests. It tells Cover-Agent which file to analyze. For example, if your source file is, you would use --source-file-path "".
  • --test-file-path: This parameter defines the path where the generated test file should be saved. Cover-Agent will write the new unit tests to this file. For example, --test-file-path "".
  • --code-coverage-report-path: This parameter indicates the path to the code coverage report file. Cover-Agent uses this report to determine the effectiveness of the generated tests and to ensure that new tests are contributing to overall coverage. For instance, --code-coverage-report-path "coverage.xml".
  • --test-command: This is the command used to run the tests. It should include any necessary flags to generate the coverage report. For example, for a Python project using pytest, you might use --test-command "pytest --cov=. --cov-report=xml --cov-report=term".
  • --test-command-dir: This parameter specifies the directory from which the test command should be run. This ensures that the tests are executed in the correct context. For example, if your tests should be run from the current directory, you would use --test-command-dir ".".
  • --coverage-type: This parameter defines the format of the coverage report, such as "cobertura". This tells Cover-Agent how to parse the coverage data. For example, --coverage-type "cobertura".
  • --desired-coverage: This sets the target code coverage percentage that you want to achieve (between 0 and 100). Cover-Agent will aim to generate tests that meet this level of coverage. For example, --desired-coverage 70 means you are aiming for 70% coverage.
  • --max-iterations: This parameter controls the maximum number of iterations to run when generating tests. Each iteration involves calling the AI model to refine the tests. Setting this to a higher number can result in more refined tests but will take more time. For example, --max-iterations 10.
Examples of Commands for Different Scenarios

To better understand how to use these parameters, let’s look at some examples for different scenarios.

Python FastAPI Example

Here’s how to run Cover-Agent for a Python FastAPI project:
A. Ensure you have the necessary files:

i. You can find the contents of this file here.


from fastapi.testclient import TestClient
from app import app

client = TestClient(app)

def test_root():
    Test the root endpoint by sending a GET request to "/" and checking the response status code and JSON body.
    response = client.get("/")
    assert response.status_code == 200
    assert response.json() == {"message": "Welcome to the FastAPI application!"}
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iii. requirements.txt:


B. Install the dependencies:

python -m venv venv
source venv/bin/activate  # On Windows, use `venv\Scripts\activate`
pip install -r requirements.txt

C. Run Cover-Agent:

cover-agent \
  --source-file-path "" \
  --test-file-path "" \
  --code-coverage-report-path "coverage.xml" \
  --test-command "pytest --cov=. --cov-report=xml --cov-report=term" \
  --test-command-dir "." \
  --coverage-type "cobertura" \
  --desired-coverage 70 \
  --max-iterations 10
Go Web Service Example

For a Go web service project:
A. Ensure you have the necessary files:

i. app.go: You can find the contents here

ii. app_test.go:

package main

import (


func TestRootEndpoint(t *testing.T) {
    router := SetupRouter() // Use the SetupRouter from app.go

    w := httptest.NewRecorder()
    req, _ := http.NewRequest("GET", "/", nil)
    router.ServeHTTP(w, req)

    assert.Equal(t, http.StatusOK, w.Code)
    assert.Contains(t, w.Body.String(), "Welcome to the Go Gin application!")
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B. Run Cover Agent:

cover-agent \
  --source-file-path "app.go" \
  --test-file-path "app_test.go" \
  --code-coverage-report-path "coverage.xml" \
  --test-command "go test -coverprofile=coverage.out && gocov convert coverage.out | gocov-xml > coverage.xml" \
  --test-command-dir $(pwd) \
  --coverage-type "cobertura" \
  --desired-coverage 70 \
  --max-iterations 1
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By following these examples and detailed explanations, you can effectively use Cover-Agent to automate your unit test generation, ensuring your codebase is robust and well-tested.

Running and Validating Tests

Once you have set up Cover-Agent and prepared your project, the next step is to run the tool and validate the generated tests. This section provides a step-by-step guide to running Cover-Agent, understanding the output files, and interpreting the test results and coverage reports.

Step-by-Step Guide to Running Cover-Agent

A. Make sure your OPENAI_API_KEY is set in your environment variables.
B. Ensure your project files are ready and all dependencies are installed.
C. Execute the command with the appropriate parameters. For example, using the Python FastAPI project:

cover-agent \
  --source-file-path "" \
  --test-file-path "" \
  --code-coverage-report-path "coverage.xml" \
  --test-command "pytest --cov=. --cov-report=xml --cov-report=term" \
  --test-command-dir "." \
  --coverage-type "cobertura" \
  --desired-coverage 70 \
  --max-iterations 10

D. Cover-Agent will interact with the OpenAI API, analyze your code, and generate tests. This process might take a few minutes depending on the complexity of your code and the number of iterations specified.

Understanding the Output Files

After running Cover-Agent, you will find several output files in your project directory. These files help you understand the prompts used, the logs generated, and the results of the tests.

  • This file contains the full prompt that was sent to the Large Language Model (LLM). It includes the context and specific instructions given to the AI for generating the unit tests.

  • run.log: This log file captures the execution details of Cover-Agent. It includes information such as the commands run, API interactions, and any errors or warnings encountered.

  • test_results.html: This HTML file presents a results table summarizing the generated tests. It includes the status of each test, failure reasons (if any), exit codes, standard output (stdout), and standard error (stderr).

Interpreting Test Results and Coverage Reports

Understanding the results and coverage reports is crucial for ensuring the effectiveness of the generated tests.

A. Test Results: The test_results.html file will show whether each generated test passed or failed. Review the failure reasons to understand why a test did not succeed. Common issues might include incorrect assumptions about the code behavior or missing edge cases.
B. Coverage Reports: The coverage report (e.g., coverage.xml) details which parts of your code are covered by tests. Tools like Cobertura or other coverage report viewers can help visualize this data.
Key Metrics include:

-Line Coverage: Percentage of lines of code executed by the tests.
-Branch Coverage: Percentage of branches (if statements, loops) executed by the tests.

C. Improving Coverage: If the desired coverage level is not met, you may need to run additional iterations or manually review and add tests for uncovered code paths. Use the insights from the and run.log to refine your prompts and commands for better results.

By following these steps and understanding the output files, you can effectively run and validate tests generated by Cover-Agent, ensuring a robust and well-tested codebase.

Benefits of Using Cover-Agent

Cover-Agent offers several significant advantages for software development teams, making the process of generating and managing unit tests more efficient and effective. Here are some key benefits:

Efficiency in Generating Unit Tests

  • Automated Test Creation: Cover-Agent leverages Generative AI to automatically generate unit tests, saving developers from the time-consuming and repetitive task of writing tests manually. This automation allows developers to focus more on coding new features and solving complex problems.
  • Rapid Test Development: The AI-driven approach significantly speeds up the test creation process, allowing for quicker iterations and faster development cycles. This means you can achieve comprehensive test coverage much more rapidly than with manual methods.

Improvement in Code Coverage and Quality

  • Enhanced Code Coverage: By generating tests systematically, Cover-Agent helps ensure that more parts of the codebase are tested. This thorough approach increases code coverage metrics, reducing the risk of undetected bugs.
  • High-Quality Tests: The tests generated by Cover-Agent are designed to be effective and thorough. They are crafted based on the structure and logic of your code, ensuring that critical paths and edge cases are covered.

Reduction in Manual Testing Effort

  • Minimized Manual Work: Developers often spend a significant amount of time writing and maintaining tests. Cover-Agent reduces this manual effort, freeing up developers to work on more value-added tasks such as feature development and performance optimization.
  • Consistency in Testing: Automated test generation ensures a consistent approach to testing across the codebase. This consistency helps in maintaining a high standard of quality and reliability in the software.

Facilitation of Continuous Integration (CI) Processes

  • Seamless Integration with CI Pipelines: Cover-Agent is designed to be integrated with popular CI platforms. This integration ensures that tests are automatically generated and executed as part of the CI process, maintaining continuous feedback on code quality.
  • Early Detection of Issues: With automated test generation and execution, potential issues can be detected early in the development cycle. This early detection helps in addressing problems before they become critical, thereby improving the overall stability and reliability of the software.

By incorporating Cover-Agent into your development workflow, you can achieve a more efficient, reliable, and streamlined testing process. This tool not only boosts productivity but also enhances the overall quality of your software, making it a valuable addition to any development team.

Community Involvement and Contributions

Cover-Agent GitHub Page

Cover-Agent is not just a tool but a collaborative project that thrives on community involvement. CodiumAI encourages developers, researchers, and enthusiasts to participate actively in the evolution of Cover-Agent. Here's how you can get involved:

  • Open-Source Development: Cover-Agent is open-source, welcoming contributions from developers around the world. This open model fosters a diverse range of ideas and innovations, leading to continuous improvement of the tool.
  • Community Engagement: By participating in the Cover-Agent community, developers can share insights, discuss best practices, and provide feedback. This engagement helps in refining the tool and making it more robust and user-friendly.
  • Collaborative Projects: Developers can collaborate on various aspects of Cover-Agent, from writing new features and improving existing functionalities to enhancing documentation and creating tutorials. This collective effort drives the project's growth and success.


Cover-Agent by CodiumAI is changing the way we approach unit testing with the help of Generative AI. This tool automates the writing of high-quality tests, boosting efficiency and improving code coverage and software quality. By cutting down on the manual effort needed for writing tests, Cover-Agent lets developers concentrate on the more innovative and creative parts of coding.

The tool integrates smoothly into CI processes and significantly enhances overall test effectiveness, making it a valuable asset for development teams. Its community-driven approach encourages contributions from developers, researchers, and enthusiasts, ensuring ongoing improvement and innovation.

Automated test generation is a major advancement in the software development lifecycle. It reduces human error, ensures comprehensive testing, and speeds up development. Cover-Agent addresses the challenges of manual test writing, making software development more efficient and reliable.

We encourage you to try Cover-Agent and see its benefits for yourself. Whether you're a developer aiming to streamline your testing workflow or a researcher exploring new testing methods, Cover-Agent provides a solid platform for innovation and collaboration. Join the Cover-Agent community, contribute to its development, and help shape the future of automated testing.

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