Make test for 3rd party imports meaningful again

.github/workflows/build.yml

@@ -73,9 +73,12 @@ jobs:
         with:
           python-version: "3.11"
       - name: Install Mitiq
+        # Since requirements.txt includes cirq, which in turn has pyquil as dependency,
+        # we explicitly remove pyquil from the installed packages after installing mitiq
         run: |
           python -m pip install --upgrade pip
           pip install .
+          pip uninstall -y pyquil
 
       - name: Test without 3rd party packages
         run: |

mitiq/benchmarks/randomized_benchmarking.py

@@ -3,8 +3,7 @@
 # module.
 # Original authors: Cirq developers: Xiao Mi, Dave Bacon, Craig Gidney,
 # Ping Yeh, Matthew Neely.
-# Code URL = ('https://github.com/quantumlib/Cirq/blob/main/cirq-core/cirq/
-# experiments/qubit_characterizations.py').
+# Code URL = ('https://github.com/quantumlib/Cirq/blob/main/cirq-core/cirq/experiments/qubit_characterizations.py').
 #
 # This source code is licensed under the GPL license (v3) found in the
 # LICENSE file in the root directory of this source tree.

mitiq/tests/test_without_third_party_packages.py

@@ -11,7 +11,9 @@
 interfaces with Mitiq (see mitiq.SUPPORTED_PROGRAM_TYPES).
 """
 
-from abc import ABCMeta
+from typing import Union, get_origin
+
+from cirq import Circuit
 
 
 def test_import():
@@ -20,14 +22,14 @@ def test_import():
     """
     import mitiq
 
-    if isinstance(mitiq.QPROGRAM, ABCMeta):
-        pass  # If only Cirq is installed, QPROGRAM is not a typing.Union.
-    else:
+    if get_origin(mitiq.QPROGRAM) is Union:
         assert (
             1  # cirq.Circuit is always supported.
             <= len(mitiq.QPROGRAM.__args__)  # All installed types.
             <= len(mitiq.SUPPORTED_PROGRAM_TYPES.keys())  # All types.
         )
+    else:
+        assert mitiq.QPROGRAM is Circuit
 
 
 # TODO: More tests wanted!