new tester; all tests categorized

tests/overflw/toverflw.nim

@@ -0,0 +1,21 @@
+discard """
+  file: "toverflw.nim"
+  output: "the computation overflowed"
+"""
+# Tests nimrod's ability to detect overflows
+
+{.push overflowChecks: on.}
+
+var
+  a, b: int
+a = high(int)
+b = -2
+try:
+  writeln(stdout, b - a)
+except EOverflow:
+  writeln(stdout, "the computation overflowed")
+
+{.pop.} # overflow check
+#OUT the computation overflowed
+
+