This looks like a great start. The only thing I'm nervous about here is the use of PortDef -- it's meant for representing the past and future states of an IO pin as strings. For something as rich as I2C, I could see that being used in one of two ways:

1. Re-implement I2C, where the PortDef strings hold the raw data you'd see on the Arduino pin. This would mean that the strings are mostly incomprehensible to the user.
2. Use a big array of PortDef (7-bit, or 128 entries in size) that corresponds to each addressable device on the bus, so you can mock each I2C address individually. Might need to explore whether the mocked I2C devices should somehow implement DeviceUsingBytes
3. Make a new structure entirely to handle all the I2C mocking

In any case, I really appreciate that you've constructed the interface for this and I'm looking forward to getting this feature ready. What are your feelings about those 3 options?

The PortDef variable was just an artefact from using the previous SPI support as a reference, and option 3 sounds correct. I have removed it, rebased and and pushed an update of the branch. I kept the removal as an additional commit, but if you want to it cost me nothing to combine the two commits into one.

BTW, I notice that you merge branches fast forward. I think it will be better to merge with non-fast forward because then you can see directly where features comes from, and also you do not need to keep old feature branches like 2019年01月06日_bugfixes, etc.

Merging branches fast-forward seems to be a new feature; I didn't realize it was enabled and it's not my preference either. I'll see what I can do with this over the next few days.

Rebased to latest version on master. Also joined the commit Remove PortDef member for wire into the main commit Minimal Wire.h mock.

Thanks. I've been giving some priority to fixing recently-reported bugs in the library, but this is still on my radar.

Sorry for the delay, I'm ready to move this forward a bit more. Does any of the PinHistory stuff I added as part of #116 make this mock easier to write? I'm still lacking a good understanding of how Wire.h is normally used, which would be a big help for me understanding how to test a library that depends on it.

Thanks. I see that are now are some conflicts relative to the latest master branch, I will rebase and resolve.

Actually I have no use cases for testing I2C communication. In my project I am using the SmartLCD library which in turn includes Wire.h in order to communicate with the hardware device. But for all practical purposes I2C is just a serial interface dependency. I have no interest in testing the SmartLCD library and do not even want to depend on that particular LCD library so I have defined an abstract LCD interface class that I use everywhere in my code except for the actual wrapper class implementation. If I want to test something related to LCD printing I will mock that interface.

class LcdInterface {
 public:
 virtual void init() = 0;
 virtual void clear() = 0;
 virtual void print(const char *msg) = 0;
 virtual void set_row_col(int row, int coloumn) = 0;
 virtual ~LcdInterface(){};
};

Thus my use case is simply not having arduino_ci fail to compile just because Wire.h is included somewhere.

Thus my use case is simply not having arduino_ci fail to compile just because Wire.h is included somewhere.

My apologies, I thought you were submitting this as a work in progress. I'll merge now and see what I can fill in.