Initial work on JSON formatter

src/spectator/command_line_arguments_config_source.cr

@@ -22,6 +22,7 @@ module Spectator
         parser.on("-l", "--line LINE", "Run examples whose line matches LINE") { |line| raise NotImplementedError.new("-l") }
         parser.on("-p", "--profile", "Display the 10 slowest specs") { raise NotImplementedError.new("-p") }
         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("--no-color", "Disable colored output") { raise NotImplementedError.new("--no-color") }

src/spectator/formatting/json_formatter.cr

@@ -0,0 +1,107 @@
+require "json"
+require "./formatter"
+
+module Spectator::Formatting
+  # Produces a JSON document containing the test results.
+  class JsonFormatter < Formatter
+    # Creates the formatter.
+    # By default, output is sent to STDOUT.
+    def initialize(io : IO = STDOUT)
+      @json = ::JSON::Builder.new(io)
+    end
+
+    # Called when a test suite is starting to execute.
+    def start_suite(suite : TestSuite)
+      @json.start_document
+      @json.start_object
+      @json.string("examples")
+      @json.start_array
+    end
+
+    # Called when a test suite finishes.
+    # The results from the entire suite are provided.
+    def end_suite(report : Report)
+      @json.end_array # examples
+      @json.end_object
+    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)
+      result.to_json(@json)
+    end
+  end
+end
+
+module Spectator
+  abstract class Result
+    def to_json(json : ::JSON::Builder)
+      json.object do
+        common_json_fields(json)
+      end
+    end
+
+    private def common_json_fields(json : ::JSON::Builder)
+      json.field("name") { example.to_json(json) }
+      json.field("location") { example.source.to_json(json) }
+      json.field("result", to_s)
+    end
+  end
+
+  abstract class FinishedResult < Result
+    def to_json(json : ::JSON::Builder)
+      json.object do
+        finished_json_fields(json)
+      end
+    end
+
+    private def finished_json_fields(json)
+      common_json_fields(json)
+      json.field("time", elapsed.to_s)
+      json.field("expectations") { expectations.to_json(json) }
+    end
+  end
+
+  abstract class Example < ExampleComponent
+    def to_json(json : ::JSON::Builder)
+      json.string(to_s)
+    end
+  end
+
+  struct Source
+    def to_json(json : ::JSON::Builder)
+      json.string(to_s)
+    end
+  end
+
+  module Expectations
+    class ExampleExpectations
+      def to_json(json : ::JSON::Builder)
+        json.array do
+          each &.to_json(json)
+        end
+      end
+    end
+
+    class Expectation
+      def to_json(json : ::JSON::Builder)
+        json.object do
+          json.field("satisfied") { satisfied?.to_json(json) }
+          json.field("expected") { expected_message.to_json(json) }
+          json.field("actual") { actual_message.to_json(json) }
+          json.field("values") do
+            json.object do
+              values.each do |labeled_value|
+                json.field(labeled_value.label, labeled_value.value.to_s)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end