AddressBook: remove unused containsTag()

AddressBook#containsTag() checks if the master list of Tags contains a
Tag with the same value as the given Tag.

This method is not used anywhere, and can be classified as unused code.
There are no commands that support it, and it is also not part of any
learning objectives. While it is used in tests, its functionality is
superseded by AddressBookTest#isTagObjectInAddressBookList(), which
checks if the master list of Tags from a given AddressBook contains the
given Tag object by reference.
AddressBookTest#isTagObjectInAddressBookList() checks if a Tag value is
in the master list like AddressBook#containsTag() does, and also checks
that Person objects points to Tag objects in the master Tag list instead
of keeping its own copies of Tags.

AddressBook#containsTag() should be removed as
unused code contributes to maintenance and comprehension overheads.

Let's remove AddressBook#containsTag().

src/seedu/addressbook/data/AddressBook.java

@@ -90,13 +90,6 @@ public boolean containsPerson(ReadOnlyPerson key) {
         return allPersons.contains(key);
     }
 
-    /**
-     * Returns true if an equivalent person exists in the address book.
-     */
-    public boolean containsTag(Tag key) {
-        return allTags.contains(key);
-    }
-
     /**
      * Removes the equivalent person from the address book.
      *

test/java/seedu/addressbook/data/AddressBookTest.java

@@ -91,12 +91,9 @@ public void addPerson_emptyAddressBook() throws Exception {
 
     @Test
     public void addPerson_someTagsNotInTagList() throws Exception {
-        assertFalse(defaultAddressBook.containsTag(tagEconomist));
-        assertFalse(defaultAddressBook.containsTag(tagPrizeWinner));
+        assertFalse(isTagObjectInAddressBookList(tagEconomist, defaultAddressBook));
+        assertFalse(isTagObjectInAddressBookList(tagPrizeWinner, defaultAddressBook));
         defaultAddressBook.addPerson(davidElliot);
-        assertTrue(defaultAddressBook.containsTag(tagEconomist));
-        assertTrue(defaultAddressBook.containsTag(tagPrizeWinner));
-
         assertTrue(isTagObjectInAddressBookList(tagEconomist, defaultAddressBook));
         assertTrue(isTagObjectInAddressBookList(tagPrizeWinner, defaultAddressBook));
     }
@@ -117,7 +114,7 @@ public void addPerson_personAlreadyInListButHasTagNotInList_tagNotAdded() throws
             // ignore expected exception
         }
 
-        assertFalse(defaultAddressBook.containsTag(tagPrizeWinner));
+        assertFalse(isTagObjectInAddressBookList(tagPrizeWinner, defaultAddressBook));
     }
 
     @Test
@@ -139,25 +136,6 @@ public void containsPerson() throws Exception {
         }
     }
 
-    @Test
-    public void containsTag() throws Exception {
-        UniqueTagList tagsWhichShouldBeIn = new UniqueTagList(tagMathematician, tagScientist);
-        UniqueTagList tagsWHichShouldNotBeIn = new UniqueTagList(tagEconomist, tagPrizeWinner);
-
-        for (Tag tagWhichShouldBeIn : tagsWhichShouldBeIn) {
-            assertTrue(defaultAddressBook.containsTag(tagWhichShouldBeIn));
-        }
-        for (Tag tagWhichShouldNotBeIn : tagsWHichShouldNotBeIn) {
-            assertFalse(defaultAddressBook.containsTag(tagWhichShouldNotBeIn));
-        }
-
-        UniqueTagList allTags = new UniqueTagList(tagPrizeWinner, tagScientist, tagMathematician, tagEconomist);
-
-        for (Tag tag : allTags) {
-            assertFalse(emptyAddressBook.containsTag(tag));
-        }
-    }
-
     @Test
     public void removePerson_personExists_removesNormally() throws Exception {
         int numberOfPersonsBeforeRemoval = getSize(defaultAddressBook.getAllPersons());