[nanopi, raspi, tinkerboard]: system.WithDigitalPinGpiodAccess() can not be overriden

[gen2thomas]

Because the option "system.WithDigitalPinGpiodAccess()" is set on constructor and there is no "system.WithDigitalPinSysfsAccess()", it is not possible to test (and unit-test) the sysfs behaviour on a board which supports gpiod. Especially all unit tests run OK on server or on machines where the feature is not activated because there is a fallback programmed to use sysfs in this case.

If unit tests of e.g. tinkerboard or nanopi platform are started on a machine with activated gpiod, the test tries to use gpiod, which can be critical for the machine, if the gpiod access rights are configured properly and the used pin is not busy. In any case this tests will fail in raspi_adaptor_test.go, tinkerboard/adaptor_test.go , nanopi/nanopi_adaptor_test.go:

• TestDigitalIO
• TestFinalizeErrorAfterGPIO

The fix should include:

• introduce "system.WithDigitalPinSysfsAccess()" to override the constructors default
• use gpiod as default in constructor for all those adaptors without the "system.WithDigitalPinGpiodAccess" call
• change all examples and unit-tests to use "system.WithDigitalPinSysfsAccess()"
• try to introduce unit-tests for gpiod (-mock, on starting with gpiod there was no simple solution for that)