Fully implemented test filtering by tags

Addresses https://gitlab.com/arctic-fox/spectator/-/issues/16

src/spectator/config.cr

@@ -20,6 +20,9 @@ module Spectator
     # Filter used to select which examples to run.
     getter node_filter : NodeFilter
 
+    # Filter used to select which examples to _not_ run.
+    getter node_reject : NodeFilter
+
     # List of hooks to run before all examples in the test suite.
     protected getter before_suite_hooks : Deque(ExampleGroupHook)
 
@@ -49,6 +52,7 @@ module Spectator
       @run_flags = source.run_flags
       @random_seed = source.random_seed
       @node_filter = source.node_filter
+      @node_reject = source.node_reject
 
       @before_suite_hooks = source.before_suite_hooks
       @before_all_hooks = source.before_all_hooks
@@ -86,7 +90,7 @@ module Spectator
 
     # Creates an iterator configured to select the filtered examples.
     def iterator(group : ExampleGroup)
-      FilteredExampleIterator.new(group, @node_filter)
+      FilteredExampleIterator.new(group, @node_filter).reject(@node_reject)
     end
 
     # Retrieves the configured random number generator.

src/spectator/config/builder.cr

@@ -19,6 +19,7 @@ module Spectator
       @primary_formatter : Formatting::Formatter?
       @additional_formatters = [] of Formatting::Formatter
       @filters = [] of NodeFilter
+      @rejects = [] of NodeFilter
 
       # List of hooks to run before all examples in the test suite.
       protected getter before_suite_hooks = Deque(ExampleGroupHook).new
@@ -263,6 +264,11 @@ module Spectator
         @filters << filter
       end
 
+      # Adds a filter to prevent examples from running.
+      def add_node_reject(filter : NodeFilter)
+        @rejects << filter
+      end
+
       # Retrieves a filter that determines which examples can run.
       # If no filters were added with `#add_node_filter`,
       # then the returned filter will allow all examples to be run.
@@ -273,6 +279,17 @@ module Spectator
         else              CompositeNodeFilter.new(filters)
         end
       end
+
+      # Retrieves a filter that prevents examples from running.
+      # If no filters were added with `#add_node_reject`,
+      # then the returned filter will allow all examples to be run.
+      protected def node_reject
+        case (filters = @rejects)
+        when .empty? then NullNodeFilter.new(false)
+        when .one?   then filters.first
+        else         CompositeNodeFilter.new(filters)
+        end
+      end
     end
   end
 end

src/spectator/config/cli_arguments_applicator.cr

@@ -148,8 +148,13 @@ module Spectator
             tag = parts.first
             value = parts.last
           end
+
           filter = TagNodeFilter.new(tag, value)
-          builder.add_node_filter(filter)
+          if negated
+            builder.add_node_reject(filter)
+          else
+            builder.add_node_filter(filter)
+          end
         end
       end
 

src/spectator/null_node_filter.cr

@@ -3,9 +3,14 @@ require "./node_filter"
 module Spectator
   # Filter that matches all nodes.
   class NullNodeFilter < NodeFilter
+    # Creates the filter.
+    # The *match* flag indicates whether all examples should match or not.
+    def initialize(@match : Bool = true)
+    end
+
     # Checks whether the node satisfies the filter.
     def includes?(_node) : Bool
-      true
+      @match
     end
   end
 end