use doAssert in tests (#16486)

tests/ccgbugs/t9286.nim

@@ -7,7 +7,7 @@ type Foo  = ref object
   i:      int
 
 proc next(foo: Foo): Option[Foo] =
-  try:    assert(foo.i == 0)
+  try:    doAssert(foo.i == 0)
   except: return      # 2º: none
   return some(foo)    # 1º: some
 
@@ -17,6 +17,6 @@ proc test =
   while isSome(opt) and foo.i < 10:
     inc(foo.i)
     opt = next(foo)   # 2º None
-  assert foo.i == 1, $foo.i
+  doAssert foo.i == 1, $foo.i
 
 test()

tests/ccgbugs/twrong_tupleconv.nim

@@ -6,7 +6,7 @@ iterator myitems*[T](a: var seq[T]): var T {.inline.} =
   while i < L:
     yield a[i]
     inc(i)
-    assert(len(a) == L, "the length of the seq changed while iterating over it")
+    doAssert(len(a) == L, "the length of the seq changed while iterating over it")
 
 # Works fine
 var xs = @[1,2,3]