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superseded by AddressBookTest#isTagObjectInAddressBookList(), and can be
replaced by the latter in these tests. AddressBook#containsTag() should
be removed as unused code contributes to maintenance and comprehension
overheads.

Let's remove AddressBook#containsTag().

ddressBookTest#isTagObjectInAddressBookList() is chosen over
AddressBook#containsTag() because the former supersedes the latter in
functionalities, and the former has to exist with or without the latter
as the former contains test-specific checks.
AddressBookTest#isTagObjectInAddressBookList() checks if the master list
of Tags from a given AddressBook contains the given Tag object by
reference, thus not only checking if a Tag value is in the master list
like AddressBook#containsTag() does, but also checks that Person objects
points to Tag objects in the master Tag list instead of keeping its own
copies of Tags. The alternative of updating AddressBook#containsTag() to
compare by reference to take over the responsibilities of
AddressBookTest#isTagObjectInAddressBookList() is inconsistent with our
API design, as it would mean adding a method used only in tests to
production code.

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());