add yield test

tests/tyield.nim

@@ -0,0 +1,31 @@
+import std/os
+
+import cps
+import cps/eventqueue
+
+const
+  start = 2
+  tiny = 0
+  big = start * 2
+var count = start
+
+proc higher(ms: int): Cont {.cps.} =
+  while count < big and count > tiny:
+    inc count
+    cps_sleep ms
+    cps_yield()
+    cps_yield()
+    cps_yield()
+
+proc lower(ms: int): Cont {.cps.} =
+  while count < big and count > tiny:
+    dec count
+    cps_sleep ms
+    cps_yield()
+
+trampoline higher(1)
+trampoline lower(1)
+
+run()
+
+assert count == tiny

tests/tyield.nim.cfg

@@ -0,0 +1,5 @@
+--path="$config/.."
+--threads:on
+--define:threadsafe
+--gc:arc
+--define:cpsDebug