Update basis equivalence test to be more specific (#6532)

This commit updates the basis translator test:
test_skip_target_basis_equivalences_1 to be more speific to the case it
was designed to test. It was originally added in #6369 as a dedicated
reproduce test to validate we fixed issue #6350 where the basis
translator was trying to translate a gate already in the basis set which
resulted in a less than ideal (but still valid) output circuit. However,
this test was written to just mirror the original issue which was part
of a larger workflow and is too broad for a dedicated test case. This is
primarily because it was running a full transpile against a backend with
the sabre swap routing pass instead of only running the basis
translator (which is what we're testing). To fix this issue with the
test this commit extracts the qasm from the transpilation into the basis
translator when running the full reproduce from the original issue and
uses that as the input circuit, then the test is updated to only run
basis translation and optimization instead of the full transpilation
against a backend. This makes the test more targetted to what it's
specifically for and stable against unrelated changes to the sabre swap
pass.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

test/python/qasm/TestBasisTranslator_skip_target.qasm

@@ -0,0 +1,99 @@
+OPENQASM 2.0;
+include "qelib1.inc";
+qreg q[5];
+h q[0];
+cu1(4.1564508) q[2],q[1];
+swap q[0],q[1];
+swap q[1],q[2];
+cx q[3],q[2];
+tdg q[2];
+swap q[3],q[4];
+cx q[3],q[2];
+t q[2];
+swap q[4],q[3];
+cx q[3],q[2];
+tdg q[2];
+t q[3];
+swap q[3],q[4];
+cx q[3],q[2];
+t q[2];
+h q[2];
+cx q[3],q[4];
+t q[3];
+tdg q[4];
+cx q[3],q[4];
+swap q[2],q[3];
+rzz(0.48622471) q[2],q[1];
+ch q[1],q[2];
+t q[1];
+swap q[0],q[1];
+id q[2];
+swap q[1],q[2];
+h q[4];
+cx q[3],q[4];
+swap q[3],q[2];
+tdg q[4];
+cx q[3],q[4];
+swap q[2],q[3];
+t q[4];
+cx q[3],q[4];
+t q[3];
+swap q[3],q[2];
+tdg q[4];
+cx q[3],q[4];
+cx q[3],q[2];
+tdg q[2];
+t q[3];
+cx q[3],q[2];
+y q[3];
+t q[3];
+h q[3];
+swap q[2],q[3];
+t q[4];
+h q[4];
+cu3(2.5787688,1.3265772,3.1398664) q[4],q[3];
+tdg q[3];
+cx q[3],q[2];
+tdg q[2];
+swap q[2],q[1];
+cx q[0],q[1];
+t q[1];
+swap q[3],q[2];
+cx q[2],q[1];
+tdg q[1];
+cx q[0],q[1];
+t q[1];
+h q[1];
+t q[2];
+swap q[2],q[1];
+cx q[0],q[1];
+t q[0];
+tdg q[1];
+cx q[0],q[1];
+u3(4.8520889,3.6025647,5.7475542) q[0];
+rz(2.1885681) q[0];
+cx q[1],q[2];
+h q[1];
+cx q[2],q[1];
+tdg q[1];
+swap q[1],q[2];
+y q[4];
+cz q[3],q[4];
+cx q[3],q[2];
+t q[2];
+cx q[1],q[2];
+t q[1];
+tdg q[2];
+cx q[3],q[2];
+t q[2];
+h q[2];
+swap q[2],q[3];
+cx q[2],q[1];
+tdg q[1];
+t q[2];
+cx q[2],q[1];
+swap q[1],q[2];
+cx q[3],q[2];
+cu3(2.7675189,4.5725211,2.9940136) q[1],q[2];
+rx(5.976651) q[4];
+cx q[4],q[3];

test/python/transpiler/test_basis_translator.py

@@ -12,7 +12,7 @@
 
 
 """Test the BasisTranslator pass"""
-
+import os
 
 from numpy import pi
 
@@ -26,7 +26,6 @@
 from qiskit.quantum_info import Operator
 from qiskit.transpiler.exceptions import TranspilerError
 from qiskit.transpiler.passes.basis import BasisTranslator, UnrollCustomDefinitions
-from qiskit.test.mock import FakeAthens
 
 
 from qiskit.circuit.library.standard_gates.equivalence_library import (
@@ -820,38 +819,16 @@ def test_condition_set_substitute_node(self):
 
     def test_skip_target_basis_equivalences_1(self):
         """Test that BasisTranslator skips gates in the target_basis - #6085"""
-
-        qstr = 'OPENQASM 2.0; \
-        include "qelib1.inc"; \
-        qreg q[5]; \
-        cu1(4.1564508) q[2],q[3]; \
-        ccx q[0],q[1],q[4]; \
-        rzz(0.48622471) q[0],q[2]; \
-        ccx q[3],q[4],q[1]; \
-        ch q[2],q[0]; \
-        y q[3]; \
-        cu3(2.5787688,1.3265772,3.1398664) q[1],q[4]; \
-        id q[0]; \
-        y q[1]; \
-        t q[2]; \
-        t q[3]; \
-        tdg q[4]; \
-        cz q[0],q[1]; \
-        ccx q[2],q[4],q[3]; \
-        rx(5.976651) q[1]; \
-        u3(4.8520889,3.6025647,5.7475542) q[2]; \
-        cswap q[0],q[3],q[4]; \
-        rz(2.1885681) q[2]; \
-        cu3(2.7675189,4.5725211,2.9940136) q[0],q[3]; \
-        cx q[1],q[4];'
         circ = QuantumCircuit()
-        circ = circ.from_qasm_str(qstr)
-
+        qasm_file = os.path.join(
+            os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
+            "qasm",
+            "TestBasisTranslator_skip_target.qasm",
+        )
+        circ = circ.from_qasm_file(qasm_file)
         circ_transpiled = transpile(
             circ,
-            backend=FakeAthens(),
             basis_gates=["id", "rz", "sx", "x", "cx"],
-            routing_method="sabre",
             seed_transpiler=42,
         )
         self.assertEqual(circ_transpiled.count_ops(), {"cx": 91, "rz": 66, "sx": 22})