example tests

contracts/Airdrop.sol

@@ -20,7 +20,7 @@ contract Airdrop is Ownable {
             "Airdrop: Recipients and amount length mismatch"
         );
         for (uint256 i = 0; i < _recipients.length; i++) {
-            IERC20(token).transfer(_recipients[i], amount[i]);
+            IERC20(token).transferFrom(msg.sender, _recipients[i], amount[i]);
         }
     }
 }

test/airdrop.test.ts

@@ -0,0 +1,73 @@
+import { SignerWithAddress } from "@nomiclabs/hardhat-ethers/signers";
+import { ethers } from "hardhat";
+import { expect } from "chai";
+import { Airdrop, MagnaToken } from "../typechain-types";
+
+describe("Airdrop", function () {
+  let token: MagnaToken;
+  let airdrop: Airdrop;
+
+  let owner: SignerWithAddress;
+  let addr1: SignerWithAddress;
+  let addr2: SignerWithAddress;
+  let addr3: SignerWithAddress;
+
+  before(async function () {
+    [owner, addr1, addr2, addr3] = await ethers.getSigners();
+
+    const Token = await ethers.getContractFactory("MagnaToken");
+    token = (await Token.deploy()) as MagnaToken;
+    await token.deployed();
+
+    const Airdrop = await ethers.getContractFactory("Airdrop");
+    airdrop = (await Airdrop.deploy(token.address)) as Airdrop;
+    await airdrop.deployed();
+  });
+
+  it("Token contract deployed", async function () {
+    expect(token.address).to.properAddress;
+  });
+
+  it("Airdrop contract deployed", async function () {
+    expect(airdrop.address).to.properAddress;
+  });
+
+  it("Airdrop contract has token address", async function () {
+    expect(await airdrop.token()).to.equal(token.address);
+  });
+
+  it("Reverts if airdropTokens is called by nonowner", async function () {
+    await expect(
+      airdrop.connect(addr1).airdropTokens([addr1.address], [100])
+    ).to.be.revertedWith("Ownable: caller is not the owner");
+  });
+
+  it("Reverts if airdropTokens is called with different length arrays", async function () {
+    await expect(
+      airdrop.airdropTokens([addr1.address], [100, 200])
+    ).to.be.revertedWith("Airdrop: Recipients and amount length mismatch");
+  });
+
+  it("Reverts if airdropTokens is called with insufficient ERC20 allownace", async function () {
+    await expect(
+      airdrop.airdropTokens([addr1.address], [100])
+    ).to.be.revertedWith("ERC20: insufficient allowance");
+  });
+
+  it("Airdrop works", async function () {
+    const balanceBefore = await token.balanceOf(owner.address);
+
+    await token.approve(airdrop.address, 600);
+    await airdrop.airdropTokens(
+      [addr1.address, addr2.address, addr3.address],
+      [100, 200, 300]
+    );
+
+    expect(await token.balanceOf(addr1.address)).to.equal(100);
+    expect(await token.balanceOf(addr2.address)).to.equal(200);
+    expect(await token.balanceOf(addr3.address)).to.equal(300);
+    expect(await token.balanceOf(owner.address)).to.equal(
+      balanceBefore.sub(600)
+    );
+  });
+});