Update tests for retainsArg

Author: natsukagami

tests/pos-custom-args/captures/i20231.scala

@@ -1,4 +1,14 @@
+import caps.cap
+
 class Async
 class C(val x: Async ?=> Unit)
 def foo(x: Async ?=> Unit): C^{x} = C(x)
-def foo(x: Async ?=> Unit)(using Async): C^{x} = C(x)
+def foo(x: Async ?=> Unit)(using Async): C^{x} = C(x)
+
+// should also work for reach and read-only capabilities
+class D(val x: Async ?=> Unit) extends caps.Mutable
+def bar1(x: Async ?=> Unit): D^{cap, x*} = D(x)
+def bar1(x: Async ?=> Unit)(using Async): D^{cap, x*} = D(x)
+def bar2(x: Async ?=> Unit): D^{cap.rd, x.rd} = D(x)
+def bar2(x: Async ?=> Unit)(using Async): D^{cap.rd, x.rd} = D(x)
+