Add Unit Test

test/hello_eth_salon.js

@@ -0,0 +1,9 @@
+var HelloEthSalon = artifacts.require("./HelloEthSalon.sol");
+
+contract("HelloEthSalon:GetMessage", function (accounts) {
+  it("should return a correct string", async function () {
+    const contract = await HelloEthSalon.deployed();
+    const result = await contract.GetMessage.call();
+    assert.isTrue(result === "I know smart contract testing!!");
+  });
+});