Fix for the prefix/suffix diff computing.

pkg/analysis_server/test/services/correction/strings_test.dart

Index: pkg/analysis_server/test/services/correction/strings_test.dart
diff --git a/pkg/analysis_server/test/services/correction/strings_test.dart b/pkg/analysis_server/test/services/correction/strings_test.dart
index ea26934a62483be78b4f6c32991e6a39851b2974..cba4315faffbc9016c472f7624ad753fd31a1e55 100644
--- a/pkg/analysis_server/test/services/correction/strings_test.dart
+++ b/pkg/analysis_server/test/services/correction/strings_test.dart
@@ -35,6 +35,27 @@ class StringsTest {
     expect(compareStrings('b', 'a'), 1);
   }
 
+  void test_findCommonOverlap() {
+    expect(findCommonOverlap('', 'abcd'), 0);
+    expect(findCommonOverlap('abc', 'abcd'), 3);
+    expect(findCommonOverlap('123456', 'abcd'), 0);
+    expect(findCommonOverlap('123456xxx', 'xxxabcd'), 3);
+    expect(findCommonOverlap('123456', '56'), 2);
+    expect(findCommonOverlap('56', '56789'), 2);
+  }
+
+  void test_findCommonPrefix() {
+    expect(findCommonPrefix('abc', 'xyz'), 0);
+    expect(findCommonPrefix('1234abcdef', '1234xyz'), 4);
+    expect(findCommonPrefix('123', '123xyz'), 3);
+  }
+
+  void test_findCommonSuffix() {
+    expect(findCommonSuffix('abc', 'xyz'), 0);
+    expect(findCommonSuffix('abcdef1234', 'xyz1234'), 4);
+    expect(findCommonSuffix('123', 'xyz123'), 3);
+  }
+
   void test_isBlank() {
     expect(isBlank(null), isTrue);
     expect(isBlank(''), isTrue);