diff_schedule tests [run_process_replay] (#5958)

* diff_schedule tests [run_process_replay]

* ok to run serial

test/external/process_replay/test_diff_schedule.py

@@ -0,0 +1,37 @@
+import unittest
+from test.external.process_replay.diff_schedule import diff_schedule
+from tinygrad import Tensor
+from tinygrad.helpers import Context
+from tinygrad.engine.schedule import SCHEDULES
+
+class TestDiffSchedule(unittest.TestCase):
+  def test_diff_arange(self):
+    # diff a single arange kernel
+    X = Tensor.randn(10, 10).realize()
+    idxs = Tensor([0, 2]).realize()
+    xt = X[idxs]
+    with Context(ARANGE_DIFF=1): xt.schedule()
+    self.assertEqual(len(SCHEDULES), 2)
+    changed = diff_schedule(SCHEDULES)
+    self.assertEqual(changed, 1)
+    SCHEDULES.clear()
+
+    # no diff
+    a = Tensor([1])+Tensor([2])
+    with Context(ARANGE_DIFF=1): a.schedule()
+    self.assertEqual(len(SCHEDULES), 2)
+    changed = diff_schedule(SCHEDULES)
+    self.assertEqual(changed, 0)
+    SCHEDULES.clear()
+
+    # no diff with two schedule creation calls
+    a = Tensor([1])+Tensor([2])
+    with Context(ARANGE_DIFF=1): a.schedule()
+    b = Tensor([3])+Tensor([4])
+    with Context(ARANGE_DIFF=1): b.schedule()
+    self.assertEqual(len(SCHEDULES), 4)
+    changed = diff_schedule(SCHEDULES)
+    self.assertEqual(changed, 0)
+
+if __name__ == '__main__':
+  unittest.main()