only match entire words

lib/girls_just_want_to_have_puns/punifier.rb

@@ -10,7 +10,7 @@ def initialize original_phrase, word_to_replace, replacement_word
     end
 
     def pun
-      new_phrase = @original_phrase.text.sub(/\b#{@word_to_replace}/i, @replacement_word)
+      new_phrase = @original_phrase.text.sub(/\b#{@word_to_replace}\b/i, @replacement_word)
       if new_phrase == @original_phrase.text
         nil
       else

spec/girls_just_want_to_have_puns/pun_generator_spec.rb

@@ -27,4 +27,18 @@
 
     expect(pun).to eq(nil)
   end
+
+  it "doesn't match partial words" do
+    generator = described_class.new(
+      "cats",
+      minimum_word_count: 6,
+      rhymes: ["bat"],
+      source_phrases: [
+        Phrase.new("misc", "throw the baby out with the bath water")
+      ]
+    )
+    pun = generator.puns.first
+
+    expect(pun).to eq(nil)
+  end
 end