Update docs

test/sanity.test.js

@@ -0,0 +1,27 @@
+const { ethers } = require('hardhat');
+const { expect } = require('chai');
+const { loadFixture, mine } = require('@nomicfoundation/hardhat-network-helpers');
+
+async function fixture() {
+  return {};
+}
+
+describe('Environment sanity', function () {
+  beforeEach(async function () {
+    Object.assign(this, await loadFixture(fixture));
+  });
+
+  describe('snapshot', function () {
+    let blockNumberBefore;
+
+    it('cache and mine', async function () {
+      blockNumberBefore = await ethers.provider.getBlockNumber();
+      await mine();
+      expect(await ethers.provider.getBlockNumber()).to.equal(blockNumberBefore + 1);
+    });
+
+    it('check snapshot', async function () {
+      expect(await ethers.provider.getBlockNumber()).to.equal(blockNumberBefore);
+    });
+  });
+});