Implement TAP formatter

src/spectator/formatting/components/tap_profile.cr

@@ -0,0 +1,32 @@
+require "../../profile"
+require "./runtime"
+
+module Spectator::Formatting::Components
+  struct TAPProfile
+    def initialize(@profile : Spectator::Profile)
+    end
+
+    def to_s(io)
+      io << "# Top "
+      io << @profile.size
+      io << " slowest examples ("
+      io << Runtime.new(@profile.time)
+      io << ", "
+      io << @profile.percentage.round(2)
+      io.puts "% of total time):"
+
+      @profile.each do |example|
+        example_profile(io, example)
+      end
+    end
+
+    private def example_profile(io, example)
+      io << "#   "
+      io.puts example
+      io << "#     "
+      io << Runtime.new(example.result.elapsed)
+      io << ' '
+      io.puts example.location
+    end
+  end
+end

src/spectator/formatting/tap_formatter.cr

@@ -1,6 +1,73 @@
 require "./formatter"
 
 module Spectator::Formatting
+  # Produces TAP output from test results.
+  # See: https://testanything.org/
+  # Version 12 of the specification is used.
   class TAPFormatter < Formatter
+    @counter = 0
+
+    # Creates the formatter.
+    def initialize(@io : IO = STDOUT)
+    end
+
+    # Invoked when the test suite begins.
+    def start(notification)
+      @io << "1.."
+      @io.puts notification.example_count
+    end
+
+    # Invoked just after an example completes.
+    def example_finished(_notification)
+      @counter += 1
+    end
+
+    # Invoked after an example completes successfully.
+    def example_passed(notification)
+      @io << "ok "
+      @io << @counter
+      @io << " - "
+      @io.puts notification.example
+    end
+
+    # Invoked after an example is skipped or marked as pending.
+    def example_pending(notification)
+      @io << "not ok " # TODO: Skipped tests should report ok.
+      @io << @counter
+      @io << " - "
+      @io << notification.example
+      @io << " # TODO "
+      @io.puts "No reason given" # TODO: Get reason from result.
+    end
+
+    # Invoked after an example fails.
+    def example_failed(notification)
+      @io << "not ok "
+      @io << @counter
+      @io << " - "
+      @io.puts notification.example
+    end
+
+    # Invoked after an example fails from an unexpected error.
+    def example_error(notification)
+      example_failed(notification)
+    end
+
+    # Called whenever the example or framework produces a message.
+    # This is typically used for logging.
+    def message(notification)
+      @io << "# "
+      @io.puts notification.message
+    end
+
+    # Invoked after testing completes with profiling information.
+    def dump_profile(notification)
+      @io << Components::TAPProfile.new(notification.profile)
+    end
+
+    # Invoked after testing completes with summarized information from the test suite.
+    def dump_summary(notification)
+      @io.puts "Bail out!" if notification.report.counts.remaining?
+    end
   end
 end