Magento – Warning: is_file() expects parameter 1 to be a valid path

This error is caused from Plug-in configuration from your custom Module, Not the _construct().

Assume you have used Plug-in and missed some method in your module.

Expected the breaking.

    $pluginMethod = 'around' . $capMethod;
    $result = $pluginInstance->$pluginMethod($this, $next, ...array_values($arguments));
    unset($pluginInstance, $pluginMethod);

Hope this helps.

I came across this and turned out to be an issue when you run integration tests at some point before running bin/magento setup:di:compile.

Integration tests generate some test modules in app/code/Magento which are then picked up by the setup:di:compile command. I fixed this by removing the Magento folder from app/code.