test: add test for capture of deferred

Author: cpcloud

koerce/tests/test_patterns.py

@@ -520,6 +520,19 @@ def test_capture():
     assert ctx == {"result": 12}
 
 
+def test_capture_with_deferred():
+    ctx = {}
+
+    x = Deferred(Variable("x"))
+    p = Capture(x, InstanceOf(float))
+
+    assert p.apply(1, context=ctx) is NoMatch
+    assert ctx == {}
+
+    assert p.apply(1.0, ctx) == 1.0
+    assert ctx == {"x": 1.0}
+
+
 def test_none_of():
     def negative(x):
         return x < 0