Add specs for partial surrogate pairs

spec/stdlib/text-utils-spec.coffee

@@ -6,12 +6,16 @@ describe 'text utilities', ->
       expect(textUtils.getCharacterCount('abc')).toBe 3
       expect(textUtils.getCharacterCount('a\uD835\uDF97b\uD835\uDF97c')).toBe 5
       expect(textUtils.getCharacterCount('\uD835\uDF97')).toBe 1
+      expect(textUtils.getCharacterCount('\uD835')).toBe 1
+      expect(textUtils.getCharacterCount('\uDF97')).toBe 1
 
   describe '.hasSurrogatePair(string)', ->
     it 'returns true when the string contains a surrogate pair', ->
       expect(textUtils.hasSurrogatePair('abc')).toBe false
       expect(textUtils.hasSurrogatePair('a\uD835\uDF97b\uD835\uDF97c')).toBe true
       expect(textUtils.hasSurrogatePair('\uD835\uDF97')).toBe true
+      expect(textUtils.hasSurrogatePair('\uD835')).toBe false
+      expect(textUtils.hasSurrogatePair('\uDF97')).toBe false
 
   describe '.isSurrogatePair(string, index)', ->
     it 'returns true when the index is the start of a high/low surrogate pair', ->
@@ -22,3 +26,5 @@ describe 'text utilities', ->
       expect(textUtils.isSurrogatePair('a\uD835\uDF97b\uD835\uDF97c', 4)).toBe true
       expect(textUtils.isSurrogatePair('a\uD835\uDF97b\uD835\uDF97c', 5)).toBe false
       expect(textUtils.isSurrogatePair('a\uD835\uDF97b\uD835\uDF97c', 6)).toBe false
+      expect(textUtils.isSurrogatePair('\uD835')).toBe false
+      expect(textUtils.isSurrogatePair('\uDF97')).toBe false

src/stdlib/text-utils.coffee

@@ -15,7 +15,7 @@ isLowSurrogate = (string, index) ->
 # index - The {Number} index to look for a surrogate pair at.
 #
 # Return a {Boolean}.
-isSurrogatePair = (string, index) ->
+isSurrogatePair = (string, index=0) ->
   isHighSurrogate(string, index) and isLowSurrogate(string, index + 1)
 
 # Get the number of characters in the string accounting for surrogate pairs.