followup nim-lang#17001: improve coverage for tests/openarray/topenar…

…ray.nim (nim-lang#17006)

* followup nim-lang#17001: improve coverage for tests/openarray/topenarray.nim

tests/openarray/topenarray.nim

@@ -2,12 +2,26 @@ discard """
   targets: "c cpp js"
 """
 
-proc pro[T](a: var openArray[T]) = discard
+proc fn1[T](a: openArray[T]): seq[T] =
+  for ai in a: result.add ai
+
+proc fn2[T](a: var openArray[T]): seq[T] =
+  for ai in a: result.add ai
+
+proc fn3[T](a: var openArray[T]) =
+  for i, ai in mpairs(a): ai = i * 10
 
 proc main =
   var a = [1,2,3,4,5]
 
-  pro(toOpenArray(a, 1, 3))
-  pro(a.toOpenArray(1,3))
+  doAssert fn1(a.toOpenArray(1,3)) == @[2,3,4]
+
+  doAssert fn2(toOpenArray(a, 1, 3)) == @[2,3,4]
+  doAssert fn2(a.toOpenArray(1,3)) == @[2,3,4]
+
+  fn3(a.toOpenArray(1,3))
+  when defined(js): discard # xxx bug #15952: `a` left unchanged
+  else: doAssert a == [1, 0, 10, 20, 5]
 
 main()
+# static: main() # xxx bug #15952: Error: cannot generate code for: mSlice