# Writing TypeScript tests

Description: Hardhat 3 Tutorial - Writing TypeScript tests

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import Run from "@hh/Run.astro";

Solidity tests are great for unit testing, but sometimes you need more complex tests that interact with multiple contracts or simulate real-world scenarios. For that, use TypeScript tests.

Create a new file at `test/Counter.ts` with the following content to write a simple TypeScript test that interacts with the `Counter` contract:

```ts {"1": 12} {"2": 16-18} {"3": 20-26} {"4": 34}
// test/Counter.ts
import assert from "node:assert/strict";
import { describe, it } from "node:test";

import { network } from "hardhat";

describe("Counter", async function () {
  const { viem } = await network.create();
  const publicClient = await viem.getPublicClient();

  it("The sum of the Increment events should match the current value", async function () {
    const counter = await viem.deployContract("Counter");
    const deploymentBlockNumber = await publicClient.getBlockNumber();

    // run a series of increments
    for (let i = 1n; i <= 10n; i++) {
      await counter.write.incBy([i]);
    }

    const events = await publicClient.getContractEvents({
      address: counter.address,
      abi: counter.abi,
      eventName: "Increment",
      fromBlock: deploymentBlockNumber,
      strict: true,
    });

    // check that the aggregated events match the current value
    let total = 0n;
    for (const event of events) {
      total += event.args.by;
    }

    assert.equal(total, await counter.read.x());
  });
});
```

This test:

1. Deploys an instance of the `Counter` contract using [Viem](https://viem.sh/).
2. Calls the `incBy` function multiple times.
3. Gets all the events emitted by the contract during those calls.
4. Checks that the sum of the `by` arguments in the `Increment` events matches the current value of `x` in the contract.

Run the TypeScript tests:

<Run command="hardhat test nodejs" />

Besides being written in TypeScript, there are two important differences between these tests and the Solidity tests you wrote earlier:

- TypeScript tests use a test runner from the TypeScript ecosystem. Hardhat works with any test runner. In this case, you're using the built-in [`node:test`](https://nodejs.org/api/test.html) module.
- While Solidity tests run directly on the EVM, TypeScript tests run on a locally simulated network. Each time a test calls `network.create()`, it gets a fresh blockchain state, and any changes made during the test are discarded at the end. This is useful for integration tests, where you want a more realistic environment with proper blocks and transactions.

You can run both Solidity and TypeScript tests together by using the main `test` task:

<Run command="hardhat test" />

:::tip
Learn more about writing tests with TypeScript and viem in [our guide](/docs/guides/testing/using-viem).
:::