I think it is because the testing software is configured to accept only a specific result, as you can see in the following code:
Failure/Error: expect($stdout).to receive(:puts).with("Hello Kent Beck!")
You can fix this by removing the extra comma that you placed in the code:
def say_hello (name = "Ruby Programming")
puts "Hello #{name}!"
end
say_hello ("Gabriela")
Now, run the code again.
It should pass, but if it fails again, try removing your call to the function,
say_hello("Gabriella")
, and run it again. Maybe the testing software is configured to accept only the specific response and nothing more than that.