Rework computing simple strings difference.

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.services.correction.strings;
 
 import 'package:analysis_server/src/services/correction/strings.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:unittest/unittest.dart' hide isEmpty;
 
@@ skipping 15 matching lines @@
   }
 
   void test_compareStrings() {
     expect(compareStrings(null, null), 0);
     expect(compareStrings(null, 'b'), 1);
     expect(compareStrings('a', null), -1);
     expect(compareStrings('a', 'b'), -1);
     expect(compareStrings('b', 'a'), 1);
   }
 
+  void test_computeSimpleDiff() {
+    assertDiff(String oldStr, String newStr) {
+      SimpleDiff diff = computeSimpleDiff(oldStr, newStr);
+      expect(diff.offset, isNonNegative);
+      expect(diff.length, isNonNegative);
+      String applied = oldStr.substring(0, diff.offset) +
+          diff.replacement +
+          oldStr.substring(diff.offset + diff.length);
+      expect(applied, newStr);
+    }
+    assertDiff('', '');
+    assertDiff('', 'a');
+    assertDiff('abc', '');
+    assertDiff('abcd', 'acd');
+    assertDiff('a', 'b');
+    assertDiff('12345xyz', '12345abcxyz');
+    assertDiff('12345xyz', '12345xyzabc');
+    assertDiff('abbc', 'abbbc');
+    assertDiff('abbbbc', 'abbbbbbc');
+  }
+
   void test_countMatches() {
     expect(countMatches(null, null), 0);
     expect(countMatches('abc', null), 0);
     expect(countMatches(null, 'abc'), 0);
     expect(countMatches('ababa', 'a'), 3);
     expect(countMatches('ababa', 'ab'), 2);
     expect(countMatches('aaabaa', 'aa'), 2);
   }
 
-  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);
@@ skipping 123 matching lines @@
     expect(repeat('abc', 3), 'abcabcabc');
   }
 
   void test_substringAfterLast() {
     expect(substringAfterLast('', '/'), '');
     expect(substringAfterLast('abc', ''), '');
     expect(substringAfterLast('abc', 'd'), 'abc');
     expect(substringAfterLast('abcbde', 'b'), 'de');
   }
 }