[Editing][CodeHealth] Improve result comparing in assert_selection

third_party/WebKit/LayoutTests/editing/assert_selection.js

Index: third_party/WebKit/LayoutTests/editing/assert_selection.js
diff --git a/third_party/WebKit/LayoutTests/editing/assert_selection.js b/third_party/WebKit/LayoutTests/editing/assert_selection.js
index 2ee74145ff63043a2113562c4e58759055572bf4..0ecd886f8ad612cec465995f90a4a7e5126b59b0 100644
--- a/third_party/WebKit/LayoutTests/editing/assert_selection.js
+++ b/third_party/WebKit/LayoutTests/editing/assert_selection.js
@@ -580,8 +580,6 @@ class Sample {
 }
 
 function assembleDescription() {
-  const RE_TEST_FUNCTION =
-      new RegExp('at Object.test \\(.*?([^/]+?):(\\d+):(\\d+)\\)');
   function getStack() {
     let stack;
     try {
@@ -591,11 +589,14 @@ function assembleDescription() {
     }
     return stack
   }
+
+  const RE_IN_ASSERT_SELECTION = new RegExp('assert_selection\\.js');
   for (const line of getStack()) {
-    const match = RE_TEST_FUNCTION.exec(line);
-    if (!match)
-      continue;
-    return `${match[1]}(${match[2]})`;
+    const match = RE_IN_ASSERT_SELECTION.exec(line);
+    if (!match) {
+      const RE_LAYOUTTESTS = new RegExp('LayoutTests.*');
+      return RE_LAYOUTTESTS.exec(line);
+    }
   }
   return '';
 }
@@ -628,6 +629,19 @@ function checkExpectedText(expectedText) {
 }
 
 /**
+ * @param {string} str1
+ * @param {string} str2
+ * @return {string}
+ */
+function commonPrefixOf(str1, str2) {
+  for (let index = 0; index < str1.length; ++index) {
+    if (str1[index] !== str2[index])
+      return str1.substr(0, index);
+  }
+  return str1;
+}
+
+/**
  * @param {string} inputText
  * @param {function(!Selection)|string}
  * @param {string} expectedText
@@ -652,9 +666,14 @@ function assertSelection(
   const actualText = sample.serialize();
   // We keep sample HTML when assertion is false for ease of debugging test
   // case.
-  if (actualText === expectedText)
+  if (actualText === expectedText) {
     sample.remove();
-  assert_equals(actualText, expectedText, description);
+    return;
+  }
+  throw new Error(`${description}\n` +
+    `\t expected ${expectedText},\n` +
+    `\t but got  ${actualText},\n` +
+    `\t sameupto ${commonPrefixOf(expectedText, actualText)}`);
 }
 
 // Export symbols