Unit testing - how do I test a function that returns random output?

Question

I have a function which takes in two parameters, and returns one or the other 50% of the time.

The unit test for this should determine that both parameters could be

Answer 1

Not sure if this is the best way, but I would use a while loop with two flags that I set based on the values I get from the function. I would also use some sort of limit so that the test doesn't go into an infinite loop if the test fails (i.e., doesn't received one of the two values). So:

int limit = 100;
int i = 0;
while(!firstValueReceived && !secondValueReceived && i < limit) {
   int value = randomFunc();

   if(!firstValueReceived) {
      firstValueReceived = (value == firstValue);
   }

   if(!secondValueReceived) {
      secondValueReceived = (value == secondValue);
   }
   i++;
}

assertTrue(firstValueReceived && secondValueReceived);

I guess you could use the test hanging as a metric to decide if it failed or not, so you could do away with the limit:

while(!firstValueReceived && !secondValueReceived) {
   int value = randomFunc();

   if(!firstValueReceived) {
      firstValueReceived = (value == firstValue);
   }

   if(!secondValueReceived) {
      secondValueReceived = (value == secondValue);
   }
}

assertTrue(firstValueReceived && secondValueReceived);