Update test script

In commit 681ef7f
I added the ability to specify a root function, instead of defaulting to
the main function, but forgot to update the test script command to use
that flag, and so some of the tests were failing.

cpp/test/run_test.py

@@ -113,7 +113,7 @@ def __init__(self, carver):
 
     def run(self, input_rel_path):
         cwd = os.getcwd()
-        completed = subprocess.run([self.carver, input_rel_path], capture_output=True, text=True)
+        completed = subprocess.run([self.carver, '-r=main', input_rel_path], capture_output=True, text=True)
         return completed.stdout if completed.stdout != None else completed.stderr
 
     def output(self, input_rel_path):