Add a Scan as a Scan sequence input test

tests/scan/test_basic.py

@@ -1110,6 +1110,23 @@ class TestScan:
 
         utt.assert_allclose(out, vR)
 
+    @pytest.mark.parametrize(
+        "mode", [Mode(linker="cvm", optimizer=None), Mode(linker="cvm")]
+    )
+    def test_sequence_is_scan(self, mode):
+        """Make sure that a `Scan` can be used as a sequence input to another `Scan`."""
+        x0 = scalar("x0")
+        scan_1, _ = scan(lambda x: x + 1, outputs_info={"initial": x0}, n_steps=10)
+        scan_2, _ = scan(lambda x: x + 1, sequences=[scan_1])
+
+        with config.change_flags(mode=mode):
+            scan_2_fn = function([x0], scan_2)
+
+        scan_2_val = scan_2_fn(0.0)
+        exp_res = np.arange(1, 11) + 1.0
+
+        assert np.array_equal(scan_2_val, exp_res)
+
     def test_grad_sitsot(self):
         def get_sum_of_grad(inp):