Add spec for runner

Added a spy for detecting when formatter methods are called.

spec/helpers/spy_formatter.cr

@@ -0,0 +1,33 @@
+# Formatter that doubles as a spy.
+# This class tracks calls made to it.
+class SpyFormatter < Spectator::Formatters::Formatter
+  {% for item in [
+                   {"start_suite", "Spectator::TestSuite"},
+                   {"end_suite", "Spectator::Report"},
+                   {"start_example", "Spectator::Example"},
+                   {"end_example", "Spectator::Result"},
+                 ] %}
+  {% method_name = item[0].id %}
+  {% argument_type = item[1].id %}
+
+  # Stores all invocations made to `#{{method_name}}`.
+  # Each element is an invocation and the value is the argument passed to the method.
+  getter {{method_name}}_calls = [] of {{argument_type}}
+
+  # Number of times the `#{{method_name}}` method was called.
+  def {{method_name}}_call_count
+    @{{method_name}}_calls.size
+  end
+
+  # Increments `#{{method_name}}_call_count` and stores the argument.
+  def {{method_name}}(arg : {{argument_type}})
+    @all_calls << {{method_name.symbolize}}
+    @{{method_name}}_calls << arg
+  end
+
+  {% end %}
+
+  # Stores the methods that were called and in which order.
+  # The symbols will be the method name (i.e. `:start_suite`).
+  getter all_calls = [] of Symbol
+end