Workaround for NoReturn type for block

Not sure if this will work for everything.
It seems that NoReturn shows up as ReturnType (generic) when the
compiler detects the block will raise.

src/spectator/test_block.cr

@@ -15,7 +15,12 @@ module Spectator
     end
 
     def self.create(proc : -> T, label : String) forall T
-      TestBlock(T).new(proc, label)
+      {% if T.id == "ReturnType".id %}
+        wrapper = -> { proc.call; nil }
+        TestBlock(Nil).new(wrapper, label)
+      {% else %}
+        TestBlock(T).new(proc, label)
+      {% end %}
     end
 
     # Creates the block expression with a generic label.
@@ -25,7 +30,12 @@ module Spectator
     end
 
     def self.create(proc : -> T) forall T
-      TestBlock(T).new(proc)
+      {% if T.id == "ReturnType".id %}
+        wrapper = -> { proc.call; nil }
+        TestBlock(Nil).new(wrapper)
+      {% else %}
+        TestBlock(T).new(proc)
+      {% end %}
     end
 
     # Reports complete information about the expression.