fix return value for unconnected signals in capture

Key Changes:
- Updated ClockedSignal.capture to return the default value for unconnected signals.
- Added unit test to verify capture behavior with default values.
- Mocked ReadOnlyManager.wait in tests to support capture verification without a simulator.

Author: RasmusGOlsen

README.md

@@ -199,8 +199,10 @@ bus = MyBus.from_pattern(dut, pattern="/u_axi_[0-9]_%/")
 
 While `from_entity` is strict, `from_pattern` allows for flexibility when the RTL structure is non-standard:
 
-- **Keyword Overrides:** Pass a signal handle as a keyword argument to skip the pattern search for that specific attribute.
-- **Indexing:** Use the `idx` argument to index into all signals discovered via the pattern (e.g., `dut.u_axi_tdata[1]`).
+- **Keyword Overrides:** Pass a signal handle as a keyword argument to skip the pattern search for that specific
+  attribute.
+- **Indexing:** Use the `idx` argument to index into all signals discovered via the pattern (e.g.,
+  `dut.u_axi_tdata[1]`).
 
 ```python
 # Connect to index 1 and manually override 'rdy'
@@ -228,8 +230,8 @@ edge and the defined input skew before returning the value.
 
 The `capture()` method accepts two optional arguments:
 
-- **`resolver`**: A resolution function (e.g., `cocotb.types.Logic.resolve`) to resolve 4-state logic values ('X', 'Z') to
-  a simpler 2-state representation.
+- **`resolver`**: A resolution function (e.g., `cocotb.types.Logic.resolve`) to resolve 4-state logic values ('X', 'Z')
+  to a simpler 2-state representation.
 - **`default`**: The value returned if the signal is an **optional signal** that is unconnected.
 
 ```python

cocotbext/interface/interface.py

@@ -112,6 +112,7 @@ async def capture(self, resolver=None, default: Any = None):
                 else:
                     logger.warning(f"{self._handle} is not resolvable")
             return value
+        return default
 
     def __getattr__(self, name):
         """Forward other cocotb handle methods (like ._name, etc)"""

tests/test_interface.py

@@ -32,7 +32,7 @@
 
 @pytest.fixture(autouse=True)
 def mock_cocotb_scheduler(monkeypatch):
-    """Auto-patch cocotb.start_soon to avoid scheduler errors in tests.
+    """Auto-patch cocotb.start_soon and ReadOnlyManager to avoid scheduler errors in tests.
 
     Properly closes coroutines to avoid RuntimeWarning about unawaited coroutines.
     """
@@ -42,7 +42,11 @@ def mock_start_soon(coro):
         if inspect.iscoroutine(coro):
             coro.close()
 
+    async def mock_wait():
+        pass
+
     monkeypatch.setattr("cocotb.start_soon", mock_start_soon)
+    monkeypatch.setattr("cocotbext.interface.interface.ReadOnlyManager.wait", mock_wait)
 
 
 # ============================================================================
@@ -577,6 +581,24 @@ async def inner():
 
         asyncio.run(inner())
 
+    def test_clocked_signal_capture_default(self, mock_hierarchy):
+        """Test capturing with a default value for unconnected signals."""
+
+        async def inner():
+            clk = mock_hierarchy._children["clk"]
+            # Signal with no handle
+            cs = ClockedSignal(None, clk, RisingEdge, is_input=True)
+
+            # Capture should return the default value
+            val = await cs.capture(default=123)
+            assert val == 123
+
+            # Capture without default should return None
+            val_none = await cs.capture()
+            assert val_none is None
+
+        asyncio.run(inner())
+
 
 # ============================================================================
 # Tests: Modport + Clocking Integration