Support tag filtering with value

src/spectator/config/cli_arguments_applicator.cr

@@ -139,11 +139,16 @@ module Spectator
 
       # Adds the tag filter option to the parser.
       private def tag_option(parser, builder)
-        parser.on("--tag TAG", "run examples with the specified TAG, or exclude examples by adding ~ before the TAG.") do |tag|
+        parser.on("--tag TAG[:VALUE]", "Run examples with the specified TAG, or exclude examples by adding ~ before the TAG.") do |tag|
           negated = tag.starts_with?('~')
           tag = tag.lchop('~')
           Log.debug { "Filtering for example with tag #{tag}" }
-          filter = TagNodeFilter.new(tag)
+          parts = tag.split(':', 2, remove_empty: true)
+          if parts.size > 1
+            tag = parts.first
+            value = parts.last
+          end
+          filter = TagNodeFilter.new(tag, value)
           builder.add_node_filter(filter)
         end
       end

src/spectator/tag_node_filter.cr

@@ -5,12 +5,12 @@ module Spectator
   class TagNodeFilter < NodeFilter
     # Creates the filter.
     # The *tag* indicates which tag the node must have in its metadata.
-    def initialize(@tag : String)
+    def initialize(@tag : String, @value : String? = nil)
     end
 
     # Checks whether the node satisfies the filter.
     def includes?(node) : Bool
-      node.metadata.each_key.any? { |key| key.to_s == @tag }
+      node.metadata.any? { |key, value| key.to_s == @tag && (!@value || value == @value) }
     end
   end
 end