Implement TAP formatter

README.md

@@ -133,7 +133,7 @@ In no particular order, features that have been implemented and are planned:
     - [X] RSpec/Crystal Spec default
     - [X] JSON
     - [ ] JUnit
-    - [ ] TAP
+    - [X] TAP
 
 ### How it Works
 

src/spectator/command_line_arguments_config_source.cr

@@ -24,7 +24,7 @@ module Spectator
         parser.on("--location FILE:LINE", "Run the example at line 'LINE' in the file 'FILE', multiple allowed") { |location| raise NotImplementedError.new("--location") }
         parser.on("--json", "Generate JSON output") { builder.formatter = Formatting::JsonFormatter.new }
         parser.on("--junit_output OUTPUT_DIR", "Generate JUnit XML output") { |output_dir| raise NotImplementedError.new("--juni_output") }
-        parser.on("--tap", "Generate TAP output (Test Anything Protocol)") { raise NotImplementedError.new("--tap") }
+        parser.on("--tap", "Generate TAP output (Test Anything Protocol)") { builder.formatter = Formatting::TAPFormatter.new }
         parser.on("--no-color", "Disable colored output") { raise NotImplementedError.new("--no-color") }
       end
     end

src/spectator/formatting/tap_formatter.cr

@@ -0,0 +1,34 @@
+module Spectator::Formatting
+  # Formatter for the "Test Anything Protocol".
+  # For details, see: https://testanything.org/
+  class TAPFormatter < Formatter
+    # Creates the formatter.
+    # By default, output is sent to STDOUT.
+    def initialize(@io : IO = STDOUT)
+      @index = 1
+    end
+
+    # Called when a test suite is starting to execute.
+    def start_suite(suite : TestSuite)
+      @io << "1.."
+      @io.puts suite.size
+    end
+
+    # Called when a test suite finishes.
+    # The results from the entire suite are provided.
+    def end_suite(report : Report)
+      @io.puts "Bail out!" if report.remaining?
+    end
+
+    # Called before a test starts.
+    def start_example(example : Example)
+    end
+
+    # Called when a test finishes.
+    # The result of the test is provided.
+    def end_example(result : Result)
+      @io.puts TAPTestLine.new(@index, result)
+      @index += 1
+    end
+  end
+end

src/spectator/formatting/tap_test_line.cr

@@ -0,0 +1,33 @@
+module Spectator::Formatting
+  # Produces a formatted TAP test line.
+  private struct TAPTestLine
+    # Creates the test line.
+    def initialize(@index : Int32, @result : Result)
+    end
+
+    # Appends the line to the output.
+    def to_s(io)
+      io << status
+      io << ' '
+      io << @index
+      io << " - "
+      io << example
+      io << " # skip" if pending?
+    end
+
+    # The text "ok" or "not ok" depending on the result.
+    private def status
+      @result.is_a?(FailedResult) ? "not ok" : "ok"
+    end
+
+    # The example that was tested.
+    private def example
+      @result.example
+    end
+
+    # Indicates whether this test was skipped.
+    private def pending?
+      @result.is_a?(PendingResult)
+    end
+  end
+end