Add helper for testing TTY output.

1 files changed, 99 insertions, 0 deletions

diff --git a/Library/Homebrew/test/support/helper/output_as_tty.rb b/Library/Homebrew/test/support/helper/output_as_tty.rb
new file mode 100644
index 000000000..bd72a8f3f
--- /dev/null
+++ b/Library/Homebrew/test/support/helper/output_as_tty.rb
@@ -0,0 +1,99 @@
+require "delegate"
+
+module Test
+  module Helper
+    module OutputAsTTY
+      module TTYTrue
+        def tty?
+          true
+        end
+
+        alias isatty tty?
+      end
+
+      # This is a custom wrapper for the `output` matcher,
+      # used for testing output to a TTY:
+      #
+      #   expect {
+      #     print "test" if $stdout.tty?
+      #   }.to output("test").to_stdout.as_tty
+      #
+      #   expect {
+      #     # command
+      #   }.to output(...).to_stderr.as_tty.with_color
+      #
+      class Output < SimpleDelegator
+        def matches?(block)
+          return super(block) unless @tty
+
+          colored_tty_block = if @output == :stdout
+            lambda do
+              $stdout.extend(TTYTrue)
+              block.call
+            end
+          elsif @output == :stderr
+            lambda do
+              $stderr.extend(TTYTrue)
+              block.call
+            end
+          else
+            raise "`as_tty` can only be chained to `stdout` or `stderr`."
+          end
+
+          return super(colored_tty_block) if @colors
+
+          uncolored_tty_block = lambda do
+            begin
+              out_stream = StringIO.new
+              err_stream = StringIO.new
+
+              old_stdout = $stdout
+              old_stderr = $stderr
+
+              $stdout = out_stream
+              $stderr = err_stream
+
+              colored_tty_block.call
+            ensure
+              $stdout = old_stdout
+              $stderr = old_stderr
+
+              $stdout.print Tty.strip_ansi(out_stream.string)
+              $stderr.print Tty.strip_ansi(err_stream.string)
+            end
+          end
+
+          super(uncolored_tty_block)
+        end
+
+        def to_stdout
+          @output = :stdout
+          super
+          self
+        end
+
+        def to_stderr
+          @output = :stderr
+          super
+          self
+        end
+
+        def as_tty
+          @tty = true
+          self
+        end
+
+        def with_color
+          @colors = true
+          return self if @tty
+          raise "`with_color` can only be chained to `as_tty`."
+        end
+      end
+
+      def output(*args)
+        core_matcher = super(*args)
+        Output.new(core_matcher)
+      end
+    end
+  end
+end