Remove verify_parallel_map script

In Qiskit#7658 we disabled multiprocessing as part of unittest runs in CI
because the multiple layers of parallelism (subprocess from stestr,
multiprocessing from qiskit, and multithreading from rust in qiskit)
were triggering a latent bug in python's multiprocessing implementation
that was blocking CI. To counter the lost coverage from disabling
multiprocessing in that PR we added a script verify_parallel_map which
force enabled multiprocessing and validated transpile() run in parallel
executed correctly. However, in Qiskit#8952 we introduced a model for
selectively enabling multiprocessing just for a single test method. This
should allow us to avoid the stochastic failure triggering the deadlock
in python's multiprocessing by overloading parallelism but still test in
isolation that parallel_map() works.

This commit builds on the test class introduced in Qiskit#8952 and adds
identical test cases to what was previously in verify_parallel_map.py to
move that coverage into the unit test suite. Then the
verify_parallel_map script is removed and all callers are updated to
just run unit tests instead of also executing that script.

.azure/test-linux.yml

@@ -93,7 +93,6 @@ jobs:
           pip install -U "cplex" "qiskit-aer" "z3-solver" -c constraints.txt
           mkdir -p /tmp/terra-tests
           cp -r test /tmp/terra-tests/.
-          cp tools/verify_parallel_map.py /tmp/terra-tests/.
           cp .stestr.conf /tmp/terra-tests/.
           cp -r .stestr /tmp/terra-tests/. || :
           sudo apt-get update
@@ -108,7 +107,6 @@ jobs:
           export PYTHONHASHSEED=$(python -S -c "import random; print(random.randint(1, 4294967295))")
           echo "PYTHONHASHSEED=$PYTHONHASHSEED"
           stestr run
-          python ./verify_parallel_map.py
           popd
         env:
           QISKIT_PARALLEL: FALSE

.azure/test-macos.yml

@@ -57,7 +57,6 @@ jobs:
           export PYTHONHASHSEED=$(python -S -c "import random; print(random.randint(1, 4294967295))")
           echo "PYTHONHASHSEED=$PYTHONHASHSEED"
           stestr run
-          python ./tools/verify_parallel_map.py
         env:
           QISKIT_PARALLEL: FALSE
           RUST_BACKTRACE: 1

.azure/test-windows.yml

@@ -48,7 +48,6 @@ jobs:
           export PYTHONHASHSEED=$(python -S -c "import random; print(random.randint(1, 1024))")
           echo "PYTHONHASHSEED=$PYTHONHASHSEED"
           stestr run
-          python ./tools/verify_parallel_map.py
         env:
           LANG: 'C.UTF-8'
           PYTHONIOENCODING: 'utf-8:backslashreplace'

.github/workflows/coverage.yml

@@ -49,16 +49,6 @@ jobs:
           QISKIT_TEST_CAPTURE_STREAMS: 1
           QISKIT_PARALLEL: FALSE
           PYTHON: "coverage3 run --source qiskit --parallel-mode"
-      - name: Generate parallel_map test
-        run: |
-          set -e
-          coverage3 run --source qiskit --parallel-mode ./tools/verify_parallel_map.py
-          ./grcov . --binary-path ./target/debug/ -s . --llvm --parallel -t lcov --branch --ignore-not-existing --ignore "/*" -o ./rust_parallel_map.info
-          mv rust_lcov/rust_unittest.info .
-        env:
-          QISKIT_TEST_CAPTURE_STREAMS: 1
-          QISKIT_PARALLEL: FALSE
-          PYTHON: "coverage3 run --source qiskit --parallel-mode"
       - name: Convert to lcov and combine data
         run: |
           set -e

test/python/compiler/test_transpiler.py

@@ -1820,3 +1820,24 @@ def test_parallel_with_target(self, opt_level):
         self.assertIsInstance(res, list)
         for circ in res:
             self.assertIsInstance(circ, QuantumCircuit)
+
+    @data(0, 1, 2, 3)
+    def test_parallel_dispatch(self, opt_level):
+        """Test that transpile in parallel works for all optimization levels."""
+        backend = FakeRueschlikon()
+        qr = QuantumRegister(16)
+        cr = ClassicalRegister(16)
+        qc = QuantumCircuit(qr, cr)
+        qc.h(qr[0])
+        for k in range(1, 15):
+            qc.cx(qr[0], qr[k])
+        qc.measure(qr, cr)
+        qlist = [qc for k in range(15)]
+        tqc = transpile(
+            qlist, backend=backend, optimization_level=opt_level, seed_transpiler=424242
+        )
+        result = backend.run(tqc, seed_simulator=4242424242, shots=1000).result()
+        counts = result.get_counts()
+        for count in counts:
+            assert math.isclose(count["0000000000000000"], 500, rel_tol=0.1)
+            assert math.isclose(count["0111111111111111"], 500, rel_tol=0.1)

tox.ini

@@ -20,7 +20,6 @@ deps = setuptools_rust  # This is work around for the bug of tox 3 (see #8606 fo
        -r{toxinidir}/requirements-dev.txt
 commands =
   stestr run {posargs}
-  {toxinidir}/tools/verify_parallel_map.py
 
 [testenv:lint]
 envdir = .tox/lint
@@ -64,7 +63,6 @@ deps = -r{toxinidir}/requirements.txt
        qiskit-aer
 commands =
   stestr run {posargs}
-  coverage3 run --source qiskit --parallel-mode {toxinidir}/tools/verify_parallel_map.py
   coverage3 combine
   coverage3 report