Add guard-tap to automate testing

Gemfile

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+source 'https://rubygems.org'
+
+gem 'guard-tap'

Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    coderay (1.0.9)
+    ffi (1.9.0)
+    formatador (0.2.4)
+    guard (1.8.1)
+      formatador (>= 0.2.4)
+      listen (>= 1.0.0)
+      lumberjack (>= 1.0.2)
+      pry (>= 0.9.10)
+      thor (>= 0.14.6)
+    guard-tap (1.2.0)
+      guard (>= 1.8)
+    listen (1.2.2)
+      rb-fsevent (>= 0.9.3)
+      rb-inotify (>= 0.9)
+      rb-kqueue (>= 0.2)
+    lumberjack (1.0.4)
+    method_source (0.8.1)
+    pry (0.9.12.2)
+      coderay (~> 1.0.5)
+      method_source (~> 0.8)
+      slop (~> 3.4)
+    rb-fsevent (0.9.3)
+    rb-inotify (0.9.0)
+      ffi (>= 0.5.0)
+    rb-kqueue (0.2.0)
+      ffi (>= 0.5.0)
+    slop (3.4.5)
+    thor (0.18.1)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  guard-tap

Guardfile

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+# A sample Guardfile
+# More info at https://github.com/guard/guard#readme
+
+guard :tap, command: 'carton exec -Ilib -- perl' do
+  watch %r{^t/.*\.t$}
+  watch %r{^(lib/.*\.pm)$} do |m|
+    modified_file = m[0]
+
+    all_test_files = Dir.glob('t/**/**.t')
+
+    all_test_files.sort_by{ |test_file|
+      # sort by similarity of path
+      a = test_file
+      b = modified_file
+      delimiter = %r{[/_\-\.]}
+      a_fragments = a.split(delimiter)
+      b_fragments = b.split(delimiter)
+      (a_fragments + b_fragments).uniq.length.to_f / (a_fragments + b_fragments).length.to_f
+    }.first
+  end
+end