Test cases - the summary

This issue is to track what this CI shield test repo covers and extend it. I would like to keep this updated ,thus take this as a first draft and based on the feedback we update it as needed, and start implementing additions/changes.

```
1. AnalogIn

Test cases

- Analog create and destroy AnalogIn object
- Analog Input on AIN0 - read() + read_u16()
- Analog Input on AIN1 - read() + read_u16()
- Analog Input on AIN2 - read() + read_u16()
- Analog Input on AIN3 - read() + read_u16()
- Analog Input on AIN4 - read() + read_u16()
- Analog Input on AIN5 - read() + read_u16()

2. AnalogOut

Test cases

- AnalogOut create and destroy AnalogOut object
- AnalogOut on AOUT - read(), write(), write_u16()

3. BusIn/Out/InOut

Test cases

- BusIn, BusOut and BusInOout create and destroy objects
- BusInOut to BusInOut - read and write, input and output
- BusIn - mode() - pullup/down

4. Digital IO

Test cases

- DigitalIn/Out create and destroy objects
- DigitalIn, Out - read/write
- mode()
- is_connected()

5. I2C

Test cases

// all below are using the default frequency
- create and destroy I2C object
- Invalid write/read (to check return values for failures)
- LM75B temperature read
- EEPROM WR single byte
- EEPROM WR 2 bytes
- EEPROM WR 10 bytes
- EEPROM WR 100 bytes

6. InterruptIn

Test cases

- create and destroy InterruptIn object
- Register callback for falling edge
- Register callback for raising edge
- enable and disable IRQ
- read() values

7. PWM

Test cases

- create and destroy PWM object
- Frequency 10ms, 30, 100 and 500ms on all PWM pins available
- Duty cycle 10, 30, 100, 500ms on all PWM pins available

8. SPI

Test cases

// assumes the default frequency
- create and destroy SPI object
- open filehandle for SD card
- write to the SD card
- read from the SD card
```

No files, test entry points, or target hardware are named. Start by reading the repository's existing CI shield tests and confirm which listed peripherals and boards are available. Define a bounded subset before implementing; done should be an agreed, runnable set of coverage for the selected cases.

Written by the indexing model from the issue text.