Introduction

This part contains test generation uses cases for your existing code. This article is part of AI-powered software development series The majority of use cases are using ChatGPT. When GitHub Copilot is, used, it will explicitly be mentioned. A lot of tests are based on my demo repository github.com/javatask/graphql-serverless. This repository is part of An efficient way to build your serverless microservices series

Note. At the time of writing the article, the capacity of ChatGPT was limited, so paid GitHubCopilot examples were added to have better experiences

Structure of use cases

I will follow the next structure:

• Description
• ChatGPT Input
• ChatGPT Output
• Output (optional)
• Copilot Input
• Copilot Output

Use cases

Test generation

Generate Unit Test with ChatGPT and Copilot

Description: Sample request to generate ChatGPT Input: "Generate Jest tests for the code"

export const getState = (text) => {
  const state = `Hello ${text}`;
  console.log("State value:", state);
  // throw error on random invocation
  if (Math.random() > 0.5) {
    throw new Error("This is an random error");
  }
  return state;
};

ChatGPT Output:

describe("getState", () => {
  test("returns the state string with text passed", () => {
    expect(getState("world")).toBe("Hello world");
  });

  test("throws an error on random invocation", () => {
    jest.spyOn(Math, "random").mockReturnValue(0.6);
    expect(getState).toThrow("This is an random error");
    Math.random.mockRestore();
  });
});

This test has an error in the first use case - getState function does not accept parameters, and you need to add spyOn Math.random to the first use case.
Using Math.random() to throw error adds complexity that is not easy to handle by AI/ After human help, it works:

Copilot Input To get tips to copilot that you want to generate a test for the function, create file state.test.js in the __tests__ directory of your NodeJS project. Then add comment // generate tests for getState, and you will get a result.

Copilot Output

describe("getState", () => {
  // test 1
  it("should return 'Hello nothing' when no env variable is set", () => {
    expect(getState()).toBe("Hello nothing");
  });
  // test 2
  it("should return 'Hello test' when env variable is set", () => {
    process.env.TEST_VAR = "test";
    expect(getState()).toBe("Hello test");
  });
}

This test suite may fail because we have a random error in the business logic.

Generate Integration Test

Description: Sample request to generate ChatGPT Input: "Generate Jest tests for the code"

export const getState = (text) => {
  const state = `Hello ${text}`;
  console.log("State value:", state);
  // throw error on random invocation
  if (Math.random() > 0.5) {
    throw new Error("This is an random error");
  }
  return state;
};

ChatGPT Output:

describe("getState", () => {
  test("returns the state string with text passed", () => {
    expect(getState("world")).toBe("Hello world");
  });

  test("throws an error on random invocation", () => {
    jest.spyOn(Math, "random").mockReturnValue(0.6);
    expect(getState).toThrow("This is an random error");
    Math.random.mockRestore();
  });
});

This test has an error in the first use case - getState function does not accept parameters, and you need to add spyOn Math.random to the first use case.
Using Math.random() to throw error adds complexity that is not easy to handle by AI/ After human help, it works:

Copilot Input To get tips to copilot that you want to generate a test for the function, create file state.test.js in the __tests__ directory of your NodeJS project. Then add comment // generate tests for getState, and you will get a result.

Copilot Output

describe("getState", () => {
  // test 1
  it("should return 'Hello nothing' when no env variable is set", () => {
    expect(getState()).toBe("Hello nothing");
  });
  // test 2
  it("should return 'Hello test' when env variable is set", () => {
    process.env.TEST_VAR = "test";
    expect(getState()).toBe("Hello test");
  });
}

This test suite may fail because we have a random error in the business logic.

Generate Performance Test

Description: To generate a test, it is worth explicitly mentioning the test framework to be used
ChatGPT Input: Generate performance test script using k6 framework for this graphql schema type Query { state: String }
ChatGPT Output:

import { makeExecutableSchema } from "graphql-tools";
import { typeDefs } from "../src/schema/state.js";
import { resolvers } from "../src/resolvers/state.js";
import gql from "graphql-tag";

const schema = makeExecutableSchema({ typeDefs, resolvers });

describe("GraphQL schema", () => {
  it("has a query for state", async () => {
    const query = gql`
      query {
        state
      }
    `;
    const result = await graphql(schema, query);
    expect(result).toEqual({
      data: {
        state: "Hello World"
      }
    });
  });
});

Output: Failed to show event after changing the syntax from CommonJS to EMS, tests fails due to absence of graphql tool. graphql-tools during 2022 migrated to new @ namespace. This shows that googling and reading throw the documentation is crucial even with AI tools.
Working test due to Apollo Blog is

import { strict as assert } from 'node:assert';
import { ApolloServer } from "@apollo/server";

import { typeDefs } from "../src/schema/state.js";
import { resolvers } from "../src/resolvers/state.js";

// This includes all tests for getAllItemsHandler()
describe("Graphql test", () => {
  it("should return Test nothing", async () => {
    const testServer = new ApolloServer({
      typeDefs,
      resolvers,
    });

    const response = await testServer.executeOperation({
      query: "query Test { state }"
    });

    // Note the use of Node's assert rather than Jest's expect; if using
    // TypeScript, `assert`` will appropriately narrow the type of `body`
    // and `expect` will not.

    assert(response.body.kind === "single");
    expect(response.body.singleResult.errors).toBeUndefined();
    expect(response.body.singleResult.data?.state).toBe("Hello nothing");
  });
});

Note. You may ask why to force ChatGPT to use graphql-tools when it can use ApolloServer to generate integration tests. I asked explicitly about graphql-tools due to the new version released in 2022 which ChatGPT and Copilot do not know.

Summary

ChatGPT and Copilot can help you write units and integration tests for existing tests. But be aware that they are limited to the knowledge that was trained on. As it was shown, both tools failed to generate tests using the latest Apollo Server or graphql-tools libs. ChatGPT can help to write performance tests using different frameworks, for this article k6 framework was used as an example.