Adjust colorization behavior to allow forced enabling of color

We want to be able to force colorized output through the presence of the
OVERCOMMIT_COLOR variable even if the output stream is not a TTY.

While here, I changed the implementation to set an instance variable
instead of checking the environment variable each time, as it is
more performant and the value of this environment variable won't change
during the course of the hook run.

Author: sds

lib/overcommit/logger.rb

@@ -11,6 +11,12 @@ def self.silent
     # @param out [IO]
     def initialize(out)
       @out = out
+      @colorize =
+        if ENV.key?('OVERCOMMIT_COLOR')
+          !%w[0 false no].include?(ENV['OVERCOMMIT_COLOR'])
+        else
+          @out.tty?
+        end
     end
 
     # Write output without a trailing newline.
@@ -78,11 +84,7 @@ def bold_warning(*args)
     # @param partial [true,false] whether to omit a newline
     def color(code, str, partial = false)
       send(partial ? :partial : :log,
-           colorize? ? "\033[#{code}m#{str}\033[0m" : str)
-    end
-
-    def colorize?
-      @out.tty? && ENV.fetch('OVERCOMMIT_COLOR', '1') != '0'
+           @colorize ? "\033[#{code}m#{str}\033[0m" : str)
     end
   end
 end

spec/overcommit/logger_spec.rb

@@ -68,6 +68,19 @@
         subject
         output.should end_with "[0m\n"
       end
+
+      context 'and colorization is disabled' do
+        around do |example|
+          Overcommit::Utils.with_environment 'OVERCOMMIT_COLOR' => '0' do
+            example.run
+          end
+        end
+
+        it 'omits the color escape sequence' do
+          subject
+          output.should_not include "\033"
+        end
+      end
     end
 
     context 'when the output stream is not a TTY' do
@@ -79,22 +92,23 @@
         subject
         output.should_not include "\033"
       end
-    end
 
-    context 'when colorization is disabled' do
-      before do
-        io.stub(:tty?).and_return(true)
-      end
+      context 'and colorization is enabled' do
+        around do |example|
+          Overcommit::Utils.with_environment 'OVERCOMMIT_COLOR' => '1' do
+            example.run
+          end
+        end
 
-      around do |example|
-        Overcommit::Utils.with_environment 'OVERCOMMIT_COLOR' => '0' do
-          example.run
+        it 'includes the color escape sequence' do
+          subject
+          output.should include "\033[#{color_code}m"
         end
-      end
 
-      it 'omits the color escape sequence' do
-        subject
-        output.should_not include "\033"
+        it 'ends with the color reset sequence' do
+          subject
+          output.should end_with "[0m\n"
+        end
       end
     end
   end