I\'m testing my application on Android P beta release 4. My app\'s targetSdkVersion is 27
It has been observed that alarm manager notifications are not
This is happening because of Power management feature introduced in Android Pie.
In android P, strict restrictions are introduced on the apps running in background. These restrictions are explained here
As we can see in the above link, if we connect the device to charging there are no restrictions imposed on the device and notifications are working properly. However, if we remove the device then Android system adds the certain restrictions for the apps running in background.
We can turn off this restrictions by turning off battery optimization for our application from device settings. Search for battery optimization in settings and turn it off for our application.
Also, testing the notifications by changing the device date and time was a hack that worked fine till now but in Android P, we've to either test them in real time scenario or turn off battery optimization for our application to test them.
I hope this will clear our doubts.