Removes stestr's grouping configuration. (#6399)

Removing  the grouping regex in .stestr.conf should allow stestr to pack its test workers better, and therefore improve the speed of test execution. However, pre-existing test cases utilizing non-unique tempfiles began to fail after the configuration change. This commit modifies such tests to pass under these new conditions. This also allows the test suite to properly execute using pytest-xdist.

Fixed #6105

.stestr.conf

@@ -1,3 +1,2 @@
 [DEFAULT]
 test_path=./test/python
-group_regex=([^\.]*\.)*

test/python/test_user_config.py

@@ -13,6 +13,7 @@
 # pylint: disable=missing-docstring
 
 import os
+from uuid import uuid4
 
 from qiskit import exceptions
 from qiskit.test import QiskitTestCase
@@ -20,9 +21,9 @@ from qiskit import user_config
 
 
 class TestUserConfig(QiskitTestCase):
-    @classmethod
-    def setUpClass(cls):
-        cls.file_path = "temp.txt"
+    def setUp(self):
+        super().setUp()
+        self.file_path = "test_%s.conf" % uuid4()
 
     def test_empty_file_read(self):
         config = user_config.UserConfig(self.file_path)

test/python/visualization/test_gate_map.py

@@ -12,8 +12,9 @@
 
 """A test for visualizing device coupling maps"""
 import unittest
-import os
 
+from io import BytesIO
+from PIL import Image
 from ddt import ddt, data
 from qiskit.test.mock import FakeProvider
 from qiskit.test import QiskitTestCase
@@ -45,11 +46,12 @@ class TestGateMap(QiskitVisualizationTestCase):
         """tests plotting of gate map of a device (20 qubit, 16 qubit, 14 qubit and 5 qubit)"""
         n = backend.configuration().n_qubits
         img_ref = path_to_diagram_reference(str(n) + "bit_quantum_computer.png")
-        filename = "temp.png"
         fig = plot_gate_map(backend)
-        fig.savefig(filename)
-        self.assertImagesAreEqual(filename, img_ref, 0.2)
-        os.remove(filename)
+        with BytesIO() as img_buffer:
+            fig.savefig(img_buffer, format="png")
+            img_buffer.seek(0)
+            self.assertImagesAreEqual(Image.open(img_buffer), img_ref, 0.2)
+        plt.close(fig)
 
     @data(*backends)
     @unittest.skipIf(not HAS_MATPLOTLIB, "matplotlib not available.")
@@ -62,11 +64,12 @@ class TestGateMap(QiskitVisualizationTestCase):
         circuit._layout.add_register(qr)
         n = backend.configuration().n_qubits
         img_ref = path_to_diagram_reference(str(n) + "_plot_circuit_layout.png")
-        filename = str(n) + "_plot_circuit_layout_result.png"
         fig = plot_circuit_layout(circuit, backend)
-        fig.savefig(filename)
-        self.assertImagesAreEqual(filename, img_ref, 0.1)
-        os.remove(filename)
+        with BytesIO() as img_buffer:
+            fig.savefig(img_buffer, format="png")
+            img_buffer.seek(0)
+            self.assertImagesAreEqual(Image.open(img_buffer), img_ref, 0.1)
+        plt.close(fig)
 
 
 @unittest.skipIf(not HAS_MATPLOTLIB, "matplotlib not available.")