Make sure the closefigures fixture is defined (#5970)

* Add missing import of matplotlib.pyplot

`test_calibration_plot_histograms` references matplotlib.pyplot,
but that module is not imported by default.

* Fix missing definition of the closefigures fixture

Problem: closefigures fixture is defined in the global conftest.py,
which is not included in cirq packages.  Package archives thus
contain tests with undefined fixture.

Solution: move closefigures definition to package conftest.py files.

* Fix function reference

Author: pavoljuhas

cirq-core/cirq/conftest.py

@@ -14,7 +14,9 @@
 
 import inspect
 import os
+
 import matplotlib.pyplot as plt
+import pytest
 
 
 def pytest_configure(config):
@@ -30,3 +32,9 @@ def pytest_pyfunc_call(pyfuncitem):
             f'{pyfuncitem._obj.__name__} is a bare async function. '
             f'It should be decorated with "@duet.sync".'
         )
+
+
+@pytest.fixture
+def closefigures():
+    yield
+    plt.close('all')

cirq-google/cirq_google/conftest.py

@@ -13,7 +13,15 @@
 # limitations under the License.
 
 import os
+import matplotlib.pyplot as plt
+import pytest
 
 
 def pytest_configure(config):
     os.environ['CIRQ_TESTING'] = "true"
+
+
+@pytest.fixture
+def closefigures():
+    yield
+    plt.close('all')

cirq-google/cirq_google/engine/calibration_test.py

@@ -16,6 +16,7 @@
 import pytest
 
 import matplotlib as mpl
+import matplotlib.pyplot as plt
 from google.protobuf.text_format import Merge
 
 import cirq
@@ -194,7 +195,7 @@ def test_calibration_heatmap():
 @pytest.mark.usefixtures('closefigures')
 def test_calibration_plot_histograms():
     calibration = cg.Calibration(_CALIBRATION_DATA)
-    _, ax = mpl.pyplot.subplots(1, 1)
+    _, ax = plt.subplots(1, 1)
     calibration.plot_histograms(['t1', 'two_qubit_xeb'], ax, labels=['T1', 'XEB'])
     assert len(ax.get_lines()) == 4
 

conftest.py

@@ -37,11 +37,3 @@ def pytest_addoption(parser):
         default=False,
         help="run Rigetti integration tests",
     )
-
-
-@pytest.fixture
-def closefigures():
-    import matplotlib.pyplot as plt
-
-    yield
-    plt.close('all')

examples/conftest.py

@@ -0,0 +1,23 @@
+# Copyright 2022 The Cirq Developers
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import matplotlib.pyplot as plt
+import pytest
+
+
+@pytest.fixture
+def closefigures():
+    yield
+    plt.close('all')