diff --git a/README.md b/README.md
index 802d397..3438019 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,7 @@ Article: https://www.sitepoint.com/getting-started-with-the-raspberry-pi-gpio-pi
 docker run -it --rm -v $(pwd):/app -w /app node:lts bash
 ~~~
 
-followed by 
+followed by
 
 ~~~shell
 npm install
@@ -21,10 +21,14 @@ npm run test
 
 ## Jest
 
-https://jestjs.io/docs/using-matchers
+- https://jestjs.io/docs/using-matchers
+- https://dev.to/zaklaughton/the-only-3-steps-you-need-to-mock-an-api-call-in-jest-39mb
+- https://jestjs.io/docs/mock-functions#mocking-modules
 
 ## TODO
 
+idea: mock functions of `onoff` to test behaviour of functions which rely on GPIO being low/high
+
 check this out: https://stackoverflow.com/questions/50066138/mock-fs-function-with-jest
 
 is this going to be a problem? https://stackoverflow.com/questions/62568294/nodejs-fs-watch-inside-docker-container-detects-changes-twice
diff --git a/action-on-gpio.js b/action-on-gpio.js
new file mode 100644
index 0000000..7c35254
--- /dev/null
+++ b/action-on-gpio.js
@@ -0,0 +1,27 @@
+const Gpio = require('onoff').Gpio;
+const mqtt = require('mqtt');
+
+const actiontrigger = {
+
+    /**
+     * those arguments should be part of the object
+     * which should also be mockabke
+     * @param {onoff.Gpio} gpio 
+     * @param {mqtt.Client} client 
+     */
+    pubMqttOnGpio (gpio, client) {
+        console.log('gpio: ');
+        if (gpio.readSync() === Gpio.LOW) {
+            client.publish('button/islow', '{true}', {qos: 1})
+        }
+        
+    },
+    
+    sleep(ms) {
+        return new Promise((resolve) => {
+            setTimeout(resolve, ms);
+        });
+    }
+}
+
+module.exports = actiontrigger
diff --git a/action-on-gpio.test.js b/action-on-gpio.test.js
new file mode 100644
index 0000000..1a8a163
--- /dev/null
+++ b/action-on-gpio.test.js
@@ -0,0 +1,16 @@
+const Gpio = require('onoff').Gpio;
+const action = require('./action-on-gpio');
+
+// https://stackoverflow.com/questions/51418086/jest-expected-mock-function-to-have-been-called-but-it-was-not-called
+describe('integration test', () => {
+    it('should publish mqtt when GPIO goes high', () => {
+        
+        const button = { readSync: jest.fn(() => Gpio.LOW)}
+        const client = { publish: jest.fn()}
+
+        action.pubMqttOnGpio(button, client);
+        expect(button.readSync).toHaveBeenCalledTimes(1)
+        expect(client.publish).toHaveBeenCalledTimes(1)
+        expect(client.publish).toBeCalledWith('button/islow', '{true}', {qos: 1})
+    })
+})
\ No newline at end of file
diff --git a/package.json b/package.json
index 6b536b7..79eb400 100644
--- a/package.json
+++ b/package.json
@@ -5,7 +5,6 @@
     "scripts": {
         "start": "node app.js",
         "test": "jest"
-
     },
     "author": {
         "name": "CR",
@@ -17,6 +16,7 @@
     },
     "dependencies": {
         "fix": "^0.0.6",
-        "mqtt": "^4.3.7"
+        "mqtt": "^4.3.7",
+        "onoff": "^6.0.3"
     }
 }