Fix issue 2084 again (#2119)

* Fix issue 2084 again

* format

* fix test

* fix test

qiskit_aer/backends/aerbackend.py

@@ -352,7 +352,7 @@ class AerBackend(Backend, ABC):
 
     def set_max_qubits(self, max_qubits):
         """Set maximun number of qubits to be used for this backend."""
-        if self._target is not None:
+        if self._target is None:
             self._configuration.n_qubits = max_qubits
 
     def clear_options(self):

releasenotes/notes/fix_issue2084-632a829da1a8dfc5.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed issue #2084 again. `backend.set_max_qubits` was not
+    properly implemented.
+    Also added test case to test this issue.
+

test/terra/primitives/test_sampler.py

@@ -270,6 +270,16 @@ class TestSampler(QiskitAerTestCase):
         result = Sampler().run(qc, shots=100).result()
         self.assertDictAlmostEqual(result.quasi_dists[0], {0: 1})
 
+    def test_truncate_large_circuit(self):
+        """Test trancate large circuit in transplier"""
+        sampler = Sampler()
+        qc = QuantumCircuit(100, 2)
+        qc.h(98)
+        qc.cx(98, 99)
+        qc.measure([98, 99], [0, 1])
+        result = sampler.run(qc).result()
+        self.assertIsInstance(result, SamplerResult)
+
 
 if __name__ == "__main__":
     unittest.main()