# Deploy contracts and run tests

In this section, you'll find everything you need to test your FHEVM smart contracts in your [Hardhat](https://hardhat.org) project.

### FHEVM Runtime Modes

The FHEVM Hardhat plugin provides three **FHEVM runtime modes** tailored for different stages of contract development and testing. Each mode offers a trade-off between speed, encryption, and persistence.

1. The **Hardhat (In-Memory)** default network: 🧪 *Uses mock encryption.* Ideal for regular tests, CI test coverage, and fast feedback during early contract development. No real encryption is used.
2. The **Hardhat Node (Local Server)** network: 🧪 *Uses mock encryption.* Ideal when you need persistent state - for example, when testing frontend interactions, simulating user flows, or validating deployments in a realistic local environment. Still uses mock encryption.
3. The **Sepolia Testnet** network: 🔐 *Uses real encryption.* Use this mode once your contract logic is stable and validated locally. This is the only mode that runs on the full FHEVM stack with **real encrypted values**. It simulates real-world production conditions but is slower and requires Sepolia ETH.

{% hint style="success" %}
**Zama Testnet** is not a blockchain itself. It is a protocol that enables you to run confidential smart contracts on existing blockchains (such as Ethereum, Base, and others) with the support of encrypted types. See the [FHE on blockchain](https://docs.zama.ai/protocol/protocol/overview) guide to learn more about the protocol architecture.

Currently, **Zama Protocol** is available on the **Sepolia Testnet**. Support for additional chains will be added in the future. [See the roadmap↗](https://docs.zama.ai/protocol/zama-protocol-litepaper#roadmap)
{% endhint %}

#### Summary

| Mode              | Encryption         | Persistent | Chain     | Speed        | Usage                                             |
| ----------------- | ------------------ | ---------- | --------- | ------------ | ------------------------------------------------- |
| Hardhat (default) | 🧪 Mock            | ❌ No       | In-Memory | ⚡⚡ Very Fast | Fast local testing and coverage                   |
| Hardhat Node      | 🧪 Mock            | ✅ Yes      | Server    | ⚡ Fast       | Frontend integration and local persistent testing |
| Sepolia Testnet   | 🔐 Real Encryption | ✅ Yes      | Server    | 🐢 Slow      | Full-stack validation with real encrypted data    |

### The FHEVM Hardhat Template

To demonstrate the three available testing modes, we'll use the [fhevm-hardhat-template](https://github.com/zama-ai/fhevm-hardhat-template), which comes with the FHEVM Hardhat Plugin pre-installed, a basic `FHECounter` smart contract, and ready-to-use tasks for interacting with a deployed instance of this contract.

### Run on Hardhat (default)

To run your tests in-memory using FHEVM mock values, simply run the following:

```sh
npx hardhat test --network hardhat
```

### Run on Hardhat Node

You can also run your tests against a local Hardhat node, allowing you to deploy contract instances and interact with them in a persistent environment.

{% stepper %}
{% step %}
**Launch the Hardhat Node server:**

* Open a new terminal window.
* From the root project directory, run the following:

```sh
npx hardhat node
```

{% endstep %}

{% step %}
**Run your test suite (optional):**

From the root project directory:

```sh
npx hardhat test --network localhost
```

{% endstep %}

{% step %}
**Deploy the `FHECounter` smart contract on Hardhat Node**

From the root project directory:

```sh
npx hardhat deploy --network localhost
```

Check the deployed contract FHEVM configuration:

```sh
npx hardhat fhevm check-fhevm-compatibility --network localhost --address <deployed contract address>
```

{% endstep %}

{% step %}
**Interact with the deployed `FHECounter` smart contract**

From the root project directory:

1. Decrypt the current counter value:

```sh
npx hardhat --network localhost task:decrypt-count
```

2. Increment the counter by 1:

```sh
npx hardhat --network localhost task:increment --value 1
```

3. Decrypt the new counter value:

```sh
npx hardhat --network localhost task:decrypt-count
```

{% endstep %}
{% endstepper %}

### Run on Sepolia Ethereum Testnet

To test your FHEVM smart contract using real encrypted values, you can run your tests on the Sepolia Testnet.

{% stepper %}
{% step %}
**Rebuild the project for Sepolia**

From the root project directory:

```sh
npx hardhat clean
npx hardhat compile --network sepolia
```

{% endstep %}

{% step %}
**Deploy the `FHECounter` smart contract on Sepolia**

```sh
npx hardhat deploy --network sepolia
```

{% endstep %}

{% step %}
**Check the deployed `FHECounter` contract FHEVM configuration**

From the root project directory:

```sh
npx hardhat fhevm check-fhevm-compatibility --network sepolia --address <deployed contract address>
```

If an internal exception is raised, it likely means the contract was not properly compiled for the Sepolia network.
{% endstep %}

{% step %}
**Interact with the deployed `FHECounter` contract**

From the root project directory:

1. Decrypt the current counter value (⏳ wait...):

```sh
npx hardhat --network sepolia task:decrypt-count
```

2. Increment the counter by 1 (⏳ wait...):

```sh
npx hardhat --network sepolia task:increment --value 1
```

3. Decrypt the new counter value (⏳ wait...):

```sh
npx hardhat --network sepolia task:decrypt-count
```

{% endstep %}
{% endstepper %}


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