Change device_count to a property

Added two more tests to test_sycl_context.py

One of them is skipped due to a bug in DPC++, which is expected to be
fixed in update 2 of oneAPI 2021

Author: oleksandr-pavlyk

dpctl/_sycl_context.pyx

@@ -207,10 +207,11 @@ cdef class SyclContext(_SyclContext):
             devices.append(SyclDevice._create(DRef))
         DPCTLDeviceVector_Delete(DVRef)
         return devices
-
+    
+    @property
     def device_count (self):
         """
-        Returns the number of sycl devices associated with SyclContext instance.
+        The number of sycl devices associated with SyclContext instance.
         """
         cdef size_t num_devs = DPCTLContext_DeviceCount(self.get_context_ref())
         if num_devs:
@@ -224,7 +225,7 @@ cdef class SyclContext(_SyclContext):
         return "SyclContext"
 
     def __repr__(self):
-        cdef size_t n = self.device_count()
+        cdef size_t n = self.device_count
         if n == 1:
             return ("<dpctl." + self.__name__ + " at {}>".format(hex(id(self))))
         else:

dpctl/tests/test_sycl_context.py

@@ -14,12 +14,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-""" Defines unit test cases for the SyclQueue class.
+""" Defines unit test cases for the SyclContxt class.
 """
 
 import dpctl
 import pytest
 
+
 list_of_standard_selectors = [
     dpctl.select_accelerator_device,
     dpctl.select_cpu_device,
@@ -358,3 +359,24 @@ def test_context_equals():
     except dpctl.SyclQueueCreationError:
         pytest.skip()
     assert ctx0.equals(ctx1)
+
+
+def test_context_can_be_used_in_queue(valid_filter):
+    try:
+        ctx = dpctl.SyclContext(valid_filter)
+    except ValueError:
+        pytest.skip()
+    devs = ctx.get_devices()
+    assert len(devs) == ctx.device_count
+    for d in devs:
+        q = dpctl.SyclQueue(ctx, d)
+
+
+@pytest.mark.xfail(reason="DPC++ bug in device equality")
+def test_context_can_be_used_in_queue2(valid_filter):
+    d = dpctl.SyclDevice(valid_filter)
+    if d.default_selector_score < 0:
+        # skip test for devices rejected by default selector
+        pytest.skip()
+    ctx = dpctl.SyclContext(d)
+    q = dpctl.SyclQueue(ctx, d)