Programmatically compile and deploy Solidity smart contracts for your tests

compile.js

const path = require("path");
const fs = require("fs");
const TruffleCompile = require("truffle-compile");

// Promisify truffle-compile
const truffleCompile = (...args) =>
  new Promise(resolve => TruffleCompile(...args, (_, data) => resolve(data)));

const compile = async filename => {
  const sourcePath = path.join(__dirname, "../contracts", filename);

  const sources = {
    [sourcePath]: fs.readFileSync(sourcePath, { encoding: "utf8" }),
  };

  const options = {
    contracts_directory: path.join(__dirname, "../contracts"),
    compilers: {
      solc: {
        version: "0.5.2",
        settings: {
          optimizer: {
            enabled: false,
            runs: 200,
          },
          evmVersion: "byzantium",
        },
      },
    },
  };

  const artifact = await truffleCompile(sources, options);
  return artifact;
};

module.exports = compile;

tests.js

/**
 * @jest-environment node
 */
const Ganache = require("ganache-core");
const Web3 = require("web3");
const compile = require("./compile");

jest.setTimeout(20000); // provide enough time to download compiler if not cached

describe("test stuff", () => {
  let contractInstance;
  let accounts;
  beforeAll(async () => {
    // 1. Compile contract artifact
    const { SimpleStorage } = await compile("SimpleStorage.sol");

    // 2. Spawn Ganache test blockchain
    const provider = Ganache.provider({ seed: "drizzle-utils" });
    const web3 = new Web3(provider);
    accounts = await web3.eth.getAccounts();

    // 3. Create initial contract instance
    const instance = new web3.eth.Contract(SimpleStorage.abi);

    // 4. Deploy contract and get new deployed Instance
    const deployedInstance = await instance
      .deploy({ data: SimpleStorage.bytecode })
      .send({ from: accounts[0], gas: 150000 });

    // Note: deployed address located at `deployedInstance._address`

    contractInstance = deployedInstance;
  });

  test("ensure test suite setup works", async () => {
    // Get old value, set a new value, check to see if it was set correctly
    const oldVal = await contractInstance.methods.get().call();
    await contractInstance.methods.set(5).send({ from: accounts[0] });
    const newVal = await contractInstance.methods.get().call();

    expect(oldVal).toBe("0");
    expect(newVal).toBe("5");
  });

});

If you want to also output the JSON artifact into a .json file, then add the following to the end of the compile function (before the return statement):

const artifactFilepath =
  sourcePath.substr(0, sourcePath.lastIndexOf(".")) + `.json`;
const artifactString = JSON.stringify(artifact, null, 4);
fs.writeFileSync(artifactFilepath, artifactString, "utf8");