Tests are important

CustomerApp.Test/CustomerListExtension.test.al

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+codeunit 50000 "HelloWorld Test"
+{
+    Subtype = Test;
+
+    [Test]
+    [HandlerFunctions('HelloWorldMessageHandler')]
+    procedure TestHelloWorldMessage()
+    var
+        CustList: TestPage "Customer List";
+    begin
+        CustList.OpenView();
+        CustList.Close();
+        if (not MessageDisplayed) then
+            ERROR('Message was not displayed!');
+    end;
+
+    [MessageHandler]
+    procedure HelloWorldMessageHandler(Message: Text[1024])
+    begin
+        MessageDisplayed := MessageDisplayed or (Message = 'App published: Hello AL-Go!');
+    end;
+
+    var
+        MessageDisplayed: Boolean;
+}
+

CustomerApp.Test/app.json

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+{
+    "id": "95243812-3ac9-4456-86aa-129f8df55db0",
+    "name": "CustomerApp.Test",
+    "publisher": "Jonas",
+    "version": "1.0.0.0",
+    "brief": "",
+    "description": "",
+    "privacyStatement": "",
+    "EULA": "",
+    "help": "",
+    "url": "",
+    "logo": "",
+    "dependencies": [
+      {
+        "publisher": "Microsoft",
+        "name": "Library Assert",
+        "id": "dd0be2ea-f733-4d65-bb34-a28f4624fb14",
+        "version": "22.0.0.0"
+      },
+      {
+        "publisher": "Microsoft",
+        "name": "Any",
+        "id": "e7320ebb-08b3-4406-b1ec-b4927d3e280b",
+        "version": "22.0.0.0"
+      }
+    ],
+    "screenshots": [],
+    "platform": "1.0.0.0",
+    "application": "22.0.0.0",
+    "idRanges": [
+      {
+        "from": 50000,
+        "to": 99999
+      }
+    ],
+    "features": [
+      "NoImplicitWith"
+    ],
+    "resourceExposurePolicy": {
+      "allowDebugging": true,
+      "allowDownloadingSource": false,
+      "includeSourceInSymbolFile": false
+    }
+  }
+