Add tests for the keepAlive option

packages/memcache-client/src/test/spec/client.spec.ts

@@ -279,6 +279,54 @@ describe("memcache client", function () {
     });
   });
 
+  it("should enable SO_KEEPALIVE with an initial delay of 60000 ms by default", async () => {
+    const _setKeepAlive = Socket.prototype.setKeepAlive;
+    const mockKeepAlive = jest.fn();
+    const x = new MemcacheClient({ server });
+
+    try {
+      Socket.prototype.setKeepAlive = mockKeepAlive;
+      await x.set("foo", "bar");
+    } finally {
+      Socket.prototype.setKeepAlive = _setKeepAlive;
+      x.shutdown();
+    }
+
+    expect(mockKeepAlive).toHaveBeenCalledWith(true, 60000);
+  });
+
+  it("should enable SO_KEEPALIVE with a custom initial delay when the keepAlive client option is a number", async () => {
+    const _setKeepAlive = Socket.prototype.setKeepAlive;
+    const mockKeepAlive = jest.fn();
+    const x = new MemcacheClient({ server, keepAlive: 10000 });
+
+    try {
+      Socket.prototype.setKeepAlive = mockKeepAlive;
+      await x.set("foo", "bar");
+    } finally {
+      Socket.prototype.setKeepAlive = _setKeepAlive;
+      x.shutdown();
+    }
+
+    expect(mockKeepAlive).toHaveBeenCalledWith(true, 10000);
+  });
+
+  it("should not enable SO_KEEPALIVE when the keepAlive client option is `false`", async () => {
+    const _setKeepAlive = Socket.prototype.setKeepAlive;
+    const mockKeepAlive = jest.fn();
+    const x = new MemcacheClient({ server, keepAlive: false });
+
+    try {
+      Socket.prototype.setKeepAlive = mockKeepAlive;
+      await x.set("foo", "bar");
+    } finally {
+      Socket.prototype.setKeepAlive = _setKeepAlive;
+      x.shutdown();
+    }
+
+    expect(mockKeepAlive).not.toHaveBeenCalled();
+  });
+
   it("should not enable TCP_NODELAY by default", async () => {
     const _setNoDelay = Socket.prototype.setNoDelay;
     const mockNoDelay = jest.fn();