Fix BasicSwap FakeRun Typo (#10274) (#10278)

* fix typo, issue #10147

* create basicswap fake_run test

* release note for #10149 fix

* ensure fake_run modifes layout prop, not the circuit logic

* black formatting, test_basic_swap

(cherry picked from commit 7df290b)

Co-authored-by: Evan McKinney <47376937+evmckinney9@users.noreply.github.com>

qiskit/transpiler/passes/routing/basic_swap.py

@@ -60,7 +60,7 @@ def run(self, dag):
             compatible with the DAG, or if the coupling_map=None.
         """
         if self.fake_run:
-            return self.fake_run(dag)
+            return self._fake_run(dag)
 
         new_dag = dag.copy_empty_like()
 

releasenotes/notes/fix-basicswap-fakerun-7469835327f6c8a1.yaml

@@ -0,0 +1,4 @@
+fixes:
+  - |
+    Fixes a typo where BasicSwap called ``fake_run()`` the attribute instead of  ``_fake_run()`` the function.
+    Refer to `#10149 <hhttps://github.com/Qiskit/qiskit-terra/issues/10147>` for more details.

test/python/transpiler/test_basic_swap.py

@@ -14,6 +14,8 @@
 
 import unittest
 from qiskit.transpiler.passes import BasicSwap
+from qiskit.transpiler.passmanager import PassManager
+from qiskit.transpiler.layout import Layout
 from qiskit.transpiler import CouplingMap, Target
 from qiskit.circuit.library import CXGate
 from qiskit.converters import circuit_to_dag
@@ -369,6 +371,43 @@ def test_far_swap_with_gate_the_middle(self):
 
         self.assertEqual(circuit_to_dag(expected), after)
 
+    def test_fake_run(self):
+        """A fake run, doesn't change dag
+        q0:--(+)-------.--
+              |        |
+        q1:---|--------|--
+              |
+        q2:---|--------|--
+              |        |
+        q3:---.--[H]--(+)-
+
+        CouplingMap map: [0]--[1]--[2]--[3]
+
+        q0:-------(+)-------.---
+                   |        |
+        q1:-----X--.--[H]--(+)--
+                |
+        q2:--X--X---------------
+             |
+        q3:--X------------------
+
+        """
+        coupling = CouplingMap([[0, 1], [1, 2], [2, 3]])
+
+        qr = QuantumRegister(4, "q")
+        circuit = QuantumCircuit(qr)
+        circuit.cx(qr[3], qr[0])
+        circuit.h(qr[3])
+        circuit.cx(qr[0], qr[3])
+
+        fake_pm = PassManager([BasicSwap(coupling, fake_run=True)])
+        real_pm = PassManager([BasicSwap(coupling, fake_run=False)])
+
+        self.assertEqual(circuit, fake_pm.run(circuit))
+        self.assertNotEqual(circuit, real_pm.run(circuit))
+        self.assertIsInstance(fake_pm.property_set["final_layout"], Layout)
+        self.assertEqual(fake_pm.property_set["final_layout"], real_pm.property_set["final_layout"])
+
 
 if __name__ == "__main__":
     unittest.main()