`AssertFunctionIsCalled` fails to unpatch target

AssertFunctionIsCalled does not exit mock.patch if the assertion fails: https://github.com/cupy/cupy/blob/c0c99108b78f4480b17cdf22ba3e903eb65f3646/cupy/testing/helper.py#L1441-L1444

As a consequence, CI reports weird failures.

Example: https://jenkins.preferred.jp/job/chainer/job/daily_master_cupy-shuffled/378/ID=20,label=mn1-p100/consoleFull

• The first failure is TestCubReduction_param_5_{backend='device', order='F', shape=(10, 20)}.test_cub_max on assert self.handle.call_count == int(self.times_called) in AssertFunctionIsCalled.__exit__.
• The second failure is TestCubReduction_param_5_{backend='device', order='F', shape=(10, 20)}.test_cub_min on assert cupy_r.shape == numpy_r.shape, where cupy_r.shape == (), numpy_r.shape == (20,).

[toslunar]

For record, the shuffle configuration (ID=20) in daily_master_cupy-shuffled/378 is

11:22:17 + ./run_cupy_combination_test.py --id 20
11:22:17 --- Shuffle Parameters ---
11:22:17 cuda_libs: ('cuda90', 'cudnn73-cuda9', 'nccl2.4-cuda9', 'none')
11:22:17 scipy: None
11:22:17 base: ubuntu16_py35
11:22:17 numpy: 1.18
11:22:17 --- Configuration ---
11:22:17 nccl: nccl2.4-cuda9
11:22:17 cutensor: none
11:22:17 cudnn: cudnn73-cuda9
11:22:17 base: ubuntu16_py35
11:22:17 cuda: cuda90
11:22:17 requires: ['numpy<1.19']
11:23:55 sha256:28646ab8950d2c4793c87a7631006aa0a7c063fd6ba98cfeef674f1c0dff3798

[takagi]

Okay. Then I’ll merge #4233 with closing this issue, and post another that addresses the first issue.