(experimental) ensure specs don't leak fibers or open ports

src/spec/methods.cr

@@ -1,4 +1,21 @@
 module Spec::Methods
+  def ensure_no_leakage(file = __FILE__, line = __LINE__)
+    lsof_initial = `lsof -p #{Process.pid} -i TCP -a 2> /dev/null`
+    fiber_count_initial = Fiber.count
+
+    yield
+
+    lsof = `lsof -p #{Process.pid} -i TCP -a 2> /dev/null`
+    diff = Fiber.count - fiber_count_initial
+
+    if lsof != lsof_initial
+      fail "Leaking open file descriptor: #{lsof}", file, line
+    end
+    if diff != 0
+      fail "Leaking #{diff} fibers (#{Fiber.count} total)", file, line
+    end
+  end
+
   # Defines an example group that describes a unit to be tested.
   # Inside *&block* examples are defined by `#it` or `#pending`.
   #
@@ -43,7 +60,9 @@ module Spec::Methods
     start = Time.monotonic
     begin
       Spec.run_before_each_hooks
-      block.call
+
+      ensure_no_leakage(file, line) { block.call }
+
       Spec::RootContext.report(:success, description, file, line, Time.monotonic - start)
     rescue ex : Spec::AssertionFailed
       Spec::RootContext.report(:fail, description, file, line, Time.monotonic - start, ex)