[Rakefile] Check fixture tarballs for pending changes

Before rebuilding tarballs or wiping changes by overwriting them by unpacking the files. This also ensures indirectly over the dependency from the spec tasks, that there will be never pending changes in the inner repo.

Rakefile

@@ -146,8 +146,18 @@ begin
     namespace :fixture_tarballs do
       task :default => :unpack
 
+      desc 'Check fixture tarballs for pending changes'
+      task :check_for_pending_changes do
+        repo_dir = 'spec/fixtures/banana-lib'
+        if Dir.exist?(repo_dir) && !Dir.chdir(repo_dir) { `git status --porcelain`.empty? }
+          puts red("[!] There are unsaved changes in '#{repo_dir}'. " \
+            'Please commit everything and run `rake spec:fixture_tarballs:rebuild`.')
+          exit 1
+        end
+      end
+
       desc 'Rebuild all the fixture tarballs'
-      task :rebuild do
+      task :rebuild => :check_for_pending_changes do
         tarballs = FileList['spec/fixtures/**/*.tar.gz']
         tarballs.each do |tarball|
           basename = File.basename(tarball)
@@ -156,7 +166,13 @@ begin
       end
 
       desc 'Unpacks all the fixture tarballs'
-      task :unpack do
+      task :unpack, :force do |_t, args|
+        begin
+          Rake::Task['spec:fixture_tarballs:check_for_pending_changes'].invoke
+        rescue SystemExit
+          exit 1 unless args[:force]
+          puts 'Continue anyway because `force` was applied.'
+        end
         tarballs = FileList['spec/fixtures/**/*.tar.gz']
         tarballs.each do |tarball|
           basename = File.basename(tarball)