moved tsets test to collections/

tests/collections/tsets.nim

@@ -0,0 +1,17 @@
+discard """
+  output: '''true
+true'''
+"""
+
+import sets
+var
+  a = initSet[int]()
+  b = initSet[int]()
+  c = initSet[string]()
+
+for i in 0..5: a.incl(i)
+for i in 1..6: b.incl(i)
+for i in 0..5: c.incl($i)
+
+echo map(a, proc(x: int): int = x + 1) == b
+echo map(a, proc(x: int): string = $x) == c