diff --git a/qiskit_ionq/exceptions.py b/qiskit_ionq/exceptions.py
index 7fc4c45..eb8cf51 100644
--- a/qiskit_ionq/exceptions.py
+++ b/qiskit_ionq/exceptions.py
@@ -151,7 +151,7 @@ def from_response(cls, response: requests.Response) -> IonQAPIError:
             error_type = error_data.get("type") or error_type
         return cls(message, status_code, headers, body, error_type)
 
-    def __init__(self, message, status_code, headers, body, error_type):
+    def __init__(self, message, status_code, headers, body, error_type):  # pylint: disable=too-many-positional-arguments
         super().__init__(message)
         self.status_code = status_code
         self.headers = headers
diff --git a/qiskit_ionq/helpers.py b/qiskit_ionq/helpers.py
index 4db5120..24b3f41 100644
--- a/qiskit_ionq/helpers.py
+++ b/qiskit_ionq/helpers.py
@@ -311,7 +311,9 @@ def get_register_sizes_and_labels(
     return sizes, labels
 
 
-def compress_to_metadata_string(metadata: dict | list) -> str:  # pylint: disable=invalid-name
+def compress_to_metadata_string(
+    metadata: dict | list,
+) -> str:  # pylint: disable=invalid-name
     """
     Convert a metadata object to a compact string format (dumped, gzipped, base64 encoded)
     for storing in IonQ API metadata
@@ -330,7 +332,9 @@ def compress_to_metadata_string(metadata: dict | list) -> str:  # pylint: disabl
     return encoded.decode()
 
 
-def decompress_metadata_string(input_string: str) -> dict | list:  # pylint: disable=invalid-name
+def decompress_metadata_string(
+    input_string: str,
+) -> dict | list:  # pylint: disable=invalid-name
     """
     Convert compact string format (dumped, gzipped, base64 encoded) from
     IonQ API metadata back into a dict or list of dicts relevant to building
@@ -541,8 +545,13 @@ def get_n_qubits(backend: str, _fallback=100) -> int:
     token = creds.get("token")
     # could use provider.get_calibration_data().get("qubits", 36)
     try:
+        target = (
+            backend.split("ionq_qpu.")[1]
+            if backend.startswith("ionq_qpu.")
+            else backend
+        )
         return requests.get(
-            url=f"{url}/characterizations/backends/{backend}/current",
+            url=f"{url}/characterizations/backends/{target}/current",
             headers={"Authorization": f"apiKey {token}"},
             timeout=5,
         ).json()["qubits"]
diff --git a/qiskit_ionq/ionq_client.py b/qiskit_ionq/ionq_client.py
index d73a769..d8d8964 100644
--- a/qiskit_ionq/ionq_client.py
+++ b/qiskit_ionq/ionq_client.py
@@ -55,9 +55,9 @@ class IonQClient:
 
     def __init__(
         self,
-        token: str | None = None,
-        url: str | None = None,
-        custom_headers: dict | None = None,
+        token: Optional[str] = None,
+        url: Optional[str] = None,
+        custom_headers: Optional[dict] = None,
     ):
         self._token = token
         self._custom_headers = custom_headers or {}
diff --git a/qiskit_ionq/ionq_job.py b/qiskit_ionq/ionq_job.py
index 579eef3..af2c90a 100644
--- a/qiskit_ionq/ionq_job.py
+++ b/qiskit_ionq/ionq_job.py
@@ -38,7 +38,7 @@
 from __future__ import annotations
 
 import warnings
-from typing import Any, Union, TYPE_CHECKING
+from typing import TYPE_CHECKING, Any, Union, Optional
 import numpy as np
 
 from qiskit import QuantumCircuit
@@ -81,7 +81,7 @@ def get_bitvalue(bitstring, bit):
 
 def _build_counts(
     data, num_qubits, clbits, shots, use_sampler=False, sampler_seed=None
-):
+):  # pylint: disable=too-many-positional-arguments
     """Map IonQ's ``counts`` onto qiskit's ``counts`` model.
 
     .. NOTE:: For simulator jobs, this method builds counts using a randomly
@@ -163,11 +163,14 @@ class IonQJob(JobV1):
     def __init__(
         self,
         backend: ionq_backend.IonQBackend,
-        job_id: str | None,
-        client: ionq_client.IonQClient | None = None,
-        circuit: QuantumCircuit | None = None,
-        passed_args: dict | None = None,
-    ):
+        job_id: Optional[str] = None,
+        client: Optional[ionq_client.IonQClient] = None,
+        circuit: Optional[QuantumCircuit] = None,
+        passed_args: Optional[dict] = None,
+    ):  # pylint: disable=too-many-positional-arguments
+        assert (
+            job_id is not None or circuit is not None
+        ), "Job must have a job_id or circuit"
         super().__init__(backend, job_id)
         self._client = client or backend.client
         self._result = None
@@ -214,7 +217,7 @@ def submit(self) -> None:
         response = self._client.submit_job(job=self)
         self._job_id = response["id"]
 
-    def get_counts(self, circuit: QuantumCircuit | None = None) -> dict:
+    def get_counts(self, circuit: Optional[QuantumCircuit] = None) -> dict:
         """Return the counts for the job.
 
         .. ATTENTION::
diff --git a/qiskit_ionq/ionq_provider.py b/qiskit_ionq/ionq_provider.py
index ff20c8d..0971bb0 100644
--- a/qiskit_ionq/ionq_provider.py
+++ b/qiskit_ionq/ionq_provider.py
@@ -30,7 +30,7 @@
 
 import logging
 
-from typing import Callable, Literal
+from typing import Callable, Literal, Optional
 
 from qiskit.providers.exceptions import QiskitBackendNotFoundError
 from qiskit.providers.providerutils import filter_backends
@@ -55,9 +55,9 @@ class IonQProvider:
 
     def __init__(
         self,
-        token: str | None = None,
-        url: str | None = None,
-        custom_headers: dict | None = None,
+        token: Optional[str] = None,
+        url: Optional[str] = None,
+        custom_headers: Optional[dict] = None,
     ):
         super().__init__()
         self.custom_headers = custom_headers
@@ -112,7 +112,7 @@ def __init__(self, backends: list[ionq_backend.Backend]):
             setattr(self, backend.name(), backend)
 
     def __call__(
-        self, name: str | None = None, filters: Callable | None = None, **kwargs
+        self, name: Optional[str] = None, filters: Optional[Callable] = None, **kwargs
     ) -> list[ionq_backend.Backend]:
         """A listing of all backends from this provider.
 
diff --git a/test/helpers/test_helpers.py b/test/helpers/test_helpers.py
index 3b4e640..a47d531 100644
--- a/test/helpers/test_helpers.py
+++ b/test/helpers/test_helpers.py
@@ -27,7 +27,9 @@
 """Test the helper functions."""
 
 import re
+from unittest.mock import patch, MagicMock
 from qiskit_ionq.ionq_client import IonQClient
+from qiskit_ionq.helpers import get_n_qubits
 
 
 def test_user_agent_header():
@@ -47,3 +49,69 @@ def test_user_agent_header():
     # Checks whether there is at-least 3 version strings from qiskit-ionq, qiskit-terra, python.
     has_all_version_strings = len(re.findall(r"\s*([\d.]+)", generated_user_agent)) >= 3
     assert all_user_agent_keywords_avail and has_all_version_strings
+
+
+def test_get_n_qubits_success():
+    """Test get_n_qubits returns correct number of qubits and checks correct URL."""
+    with patch("requests.get") as mock_get:
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"qubits": 11}
+        mock_get.return_value = mock_response
+
+        backend = "ionq_qpu.aria-1"
+        result = get_n_qubits(backend)
+
+        expected_url = (
+            "https://api.ionq.co/v0.3/characterizations/backends/aria-1/current"
+        )
+
+        # Create a regular expression to match the Authorization header with an apiKey
+        expected_headers = {"Authorization": re.compile(r"apiKey\s+\S+")}
+
+        # Check the arguments of the last call to `requests.get`
+        mock_get.assert_called()
+        _, kwargs = mock_get.call_args
+        assert (
+            kwargs["url"] == expected_url
+        ), f"Expected URL {expected_url}, but got {kwargs['url']}"
+
+        # Assert that the headers contain the apiKey in the expected format
+        assert re.match(
+            expected_headers["Authorization"], kwargs["headers"]["Authorization"]
+        ), (
+            f"Expected headers to match {expected_headers['Authorization'].pattern}, "
+            f"but got {kwargs['headers']['Authorization']}"
+        )
+
+        assert result == 11, f"Expected 11 qubits, but got {result}"
+
+
+def test_get_n_qubits_fallback():
+    """Test get_n_qubits returns fallback number of qubits and checks correct URL on failure."""
+    with patch("requests.get", side_effect=Exception("Network error")) as mock_get:
+        backend = "aria-1"
+        result = get_n_qubits(backend)
+
+        expected_url = (
+            "https://api.ionq.co/v0.3/characterizations/backends/aria-1/current"
+        )
+
+        # Create a regular expression to match the Authorization header with an apiKey
+        expected_headers = {"Authorization": re.compile(r"apiKey\s+\S+")}
+
+        # Check the arguments of the last call to `requests.get`
+        mock_get.assert_called()
+        _, kwargs = mock_get.call_args
+        assert (
+            kwargs["url"] == expected_url
+        ), f"Expected URL {expected_url}, but got {kwargs['url']}"
+
+        # Assert that the headers contain the apiKey in the expected format
+        assert re.match(
+            expected_headers["Authorization"], kwargs["headers"]["Authorization"]
+        ), (
+            f"Expected headers to match {expected_headers['Authorization'].pattern}, "
+            f"but got {kwargs['headers']['Authorization']}"
+        )
+
+        assert result == 100, f"Expected fallback of 100 qubits, but got {result}"
diff --git a/tox.ini b/tox.ini
index 14d6c26..8cc1460 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,6 +18,7 @@ setenv =
   VIRTUAL_ENV={envdir}
   LANGUAGE=en_US
   LC_ALL=en_US.utf-8
+commands = pytest
 
 [testenv:lint]
 deps =