How can I test Arduino code that doesn't return values

Question

The question is maybe not explicit enough.
I'm trying to write tests for an Arduino program, using VSCode with Platformio.

Here is an example of a function I want to test:

#include "flash.h"
#include <Arduino.h>

void flashXTimes(
    uint8_t LEDPin,
    uint16_t numberOfFlashes,
    uint16_t onDuration,
    uint16_t offDuration)
{
  for (uint16_t i = 0; i < numberOfFlashes; i++)
  {
    digitalWrite(LEDPin, HIGH);
    delay(onDuration);
    digitalWrite(LEDPin, LOW);
    delay(offDuration);
  }
}

I want to check that when I call this function with numberOfFlashes 3, it will actually flash 3 times. Sure the code is so easy that tests aren't really needed, but I want to do them anyway.

So ChatGPT gave me a hint of using a mock digital write

static uint32_t digitalWriteCalls = 0;
void digitalWriteMock(uint8_t pin, uint8_t val) {
    digitalWriteCalls++;
}

but then told me to digitalWrite = &digitalWriteMock; which would work fine in Python, but not in C++.

By following the Platformio testing guide using Unity, I got tests going, but nothing meaningful.
I'd appreciate some help in getting started with testing in C++/Arduino

If I understand what you want, then you have to run the test on a test 'framework'. for the test on PC you can't use Arduino core's Arduino.h, you have to write your own Arduino.h with a different implementation of digitalWrite — Juraj, Mar 18 '23 at 15:41
@Juraj you can actually run tests on the Arduino with Platformio and Unity: https://docs.platformio.org/en/stable/advanced/unit-testing/runner.html#remote-test-runner — Thomas J, Mar 18 '23 at 16:03
but for that you don't need to add a mock function to your sketch. https://docs.platformio.org/en/stable/advanced/unit-testing/runner.html#embedded — Juraj, Mar 18 '23 at 16:57
what I want to test is how many times digitalWrite was called — Thomas J, Mar 18 '23 at 17:00

score 0 · Answer 1 · answered Mar 18 '23 at 15:11

0

Following up to ChatGPT's answer, you'd want to define a variable of type "pointer to function". When you test, that variable points to the test function. When you run "for real", that variable points to the real function.

For example:

void (*digitalWriteFunction)(uint8_t, uint8_t);
if (testing) {
    digitalWriteFunction = &digitalWriteMock;
}
else {
    digitalWriteFunction = &digitalWrite;
}

// From here on, use digitalWriteFunction pretty much the same way you'd call a function:
(*digitalWriteFunction)(LEDPin, HIGH);

Obviously, in your mock function, you can do whatever you want like confirm what are the values of the arguments passed, etc.

answered Mar 18 '23 at 15:11

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Thanks, that helped me a bit already, I made it work in the test file with #ifdef PIO_UNIT_TESTING and a simple digitalWriteFunction(LED_BUILTIN, HIGH); and could assert that afterwards digitalWriteCalls==1. But for some reason I don't understand, if I do it in my flash.cpp file, and I include flash.h in my test file, I get undefined reference to `flashXTimes` – Thomas J Mar 18 '23 at 16:20
I managed to add the mock conditionally in my code, so in "production" mode everything works fine. In testing, the Arduino seems to freeze – Thomas J Mar 18 '23 at 16:47
Found out that as soon as I use the delay function, the communication between the Arduino and platformio will break – Thomas J Mar 18 '23 at 17:20

How can I test Arduino code that doesn't return values

1 Answers1