Implement random generator and seed

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("--seed INTEGER", "Set the seed for the random number generator") { |seed| builder.seed = seed.to_i }
         parser.on("--json", "Generate JSON output") { builder.formatter = Formatting::JsonFormatter.new }
         parser.on("--junit_output OUTPUT_DIR", "Generate JUnit XML output") { |output_dir| builder.add_formatter(Formatting::JUnitFormatter.new(output_dir)) }
         parser.on("--tap", "Generate TAP output (Test Anything Protocol)") { builder.formatter = Formatting::TAPFormatter.new }

src/spectator/config.cr

@@ -13,12 +13,16 @@ module Spectator
     # Examples won't run, but the output will show that they did.
     getter? dry_run : Bool
 
+    # Seed for the random number generator.
+    getter seed : Int32
+
     # Creates a new configuration.
     def initialize(builder)
       @formatters = builder.formatters
       @fail_fast = builder.fail_fast?
       @fail_blank = builder.fail_blank?
       @dry_run = builder.dry_run?
+      @seed = builder.seed
     end
 
     # Yields each formatter that should be reported to.

src/spectator/config_builder.cr

@@ -8,6 +8,9 @@ module Spectator
       new.build
     end
 
+    # Seed for the random number generator.
+    property seed = 0
+
     @primary_formatter : Formatting::Formatter?
     @additional_formatters = [] of Formatting::Formatter
     @fail_fast = false