Add base classes for defining example run order

src/spectator.cr

@@ -16,6 +16,6 @@ module Spectator
   end
 
   at_exit do
-    Runner.new(ALL_EXAMPLES).run
+    Runner.new(ALL_EXAMPLES, DefinedRunOrder.new).run
   end
 end

src/spectator/defined_run_order.cr

@@ -0,0 +1,9 @@
+require "./run_order"
+
+module Spectator
+  private class DefinedRunOrder < RunOrder
+    def sort(a : Example, b : Example) : Int32
+      -1
+    end
+  end
+end

src/spectator/run_order.cr

@@ -0,0 +1,5 @@
+module Spectator
+  private abstract class RunOrder
+    abstract def sort(a : Example, b : Example) : Int32
+  end
+end

src/spectator/runner.cr

@@ -5,17 +5,21 @@ module Spectator
   class Runner
     getter results : Enumerable(ExampleResult)
 
-    def initialize(@examples : Enumerable(Example))
+    def initialize(@examples : Enumerable(Example), @run_order : RunOrder)
       @results = Array(ExampleResult).new(@examples.size)
     end
 
     def run : Nil
-      @examples.each do |example|
+      sorted_examples.each do |example|
         result = run_example(example)
         pp result
       end
     end
 
+    private def sorted_examples
+      @examples.to_a.sort { |a, b| @run_order.sort(a, b) }
+    end
+
     private def run_example(example)
       example.run
       SuccessfulExampleResult.new(example)