code: def flatten_tests(test_classes):
      """
      >>> test_classes = {x: [x] for x in range(5)}
      >>> flatten_tests(test_classes)
      [(0, 0), (1, 1), (2, 2), (3, 3), (4, 4)]
      >>> test_classes = {x: [x + 1, x + 2] for x in range(2)}
      >>> flatten_tests(test_classes)
      [(0, 1), (0, 2), (1, 2), (1, 3)]
      """
      tests = []
      for class_name, test_names in test_classes.items():
          tests += [(class_name, test_name) for test_name in test_names]
      return tests
  
imports: import collections
label_desc: Use image node_id 1 for calling a global function with example usage: flatten_tests(test_classes) and returns: tests