assert: reduce diff noise

Assertion errors that produce a diff show a diff for identical entries
in case one side of the comparison has more object properties than the
other one. Those lines are now taken into account and will not show up
as diverging lines anymore.

Refs: https://github.com/nodejs/node/issues/22763

PR-URL: https://github.com/nodejs/node/pull/23048
Refs: https://github.com/nodejs/node/issues/22763
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

2 files changed, 50 insertions, 29 deletions

diff --git a/lib/internal/assert.js b/lib/internal/assert.js
index 92c2a1d0af..d3155cf692 100644
--- a/lib/internal/assert.js
+++ b/lib/internal/assert.js
@@ -205,29 +205,42 @@ function createErrDiff(actual, expected, operator) {
       res += `\n${green}+${white} ${actualLines[i]}`;
       printedLines++;
     // Lines diverge
-    } else if (actualLines[i] !== expectedLines[i]) {
-      if (cur > 1 && i > 2) {
-        if (cur > 4) {
-          res += `\n${blue}...${white}`;
-          skipped = true;
-        } else if (cur > 3) {
-          res += `\n  ${actualLines[i - 2]}`;
+    } else {
+      const expectedLine = expectedLines[i];
+      let actualLine = actualLines[i];
+      let divergingLines = actualLine !== expectedLine &&
+                           (!actualLine.endsWith(',') ||
+                            actualLine.slice(0, -1) !== expectedLine);
+      if (divergingLines &&
+          expectedLine.endsWith(',') &&
+          expectedLine.slice(0, -1) === actualLine) {
+        divergingLines = false;
+        actualLine += ',';
+      }
+      if (divergingLines) {
+        if (cur > 1 && i > 2) {
+          if (cur > 4) {
+            res += `\n${blue}...${white}`;
+            skipped = true;
+          } else if (cur > 3) {
+            res += `\n  ${actualLines[i - 2]}`;
+            printedLines++;
+          }
+          res += `\n  ${actualLines[i - 1]}`;
+          printedLines++;
+        }
+        lastPos = i;
+        res += `\n${green}+${white} ${actualLine}`;
+        other += `\n${red}-${white} ${expectedLine}`;
+        printedLines += 2;
+      // Lines are identical
+      } else {
+        res += other;
+        other = '';
+        if (cur === 1 || i === 0) {
+          res += `\n  ${actualLine}`;
           printedLines++;
         }
-        res += `\n  ${actualLines[i - 1]}`;
-        printedLines++;
-      }
-      lastPos = i;
-      res += `\n${green}+${white} ${actualLines[i]}`;
-      other += `\n${red}-${white} ${expectedLines[i]}`;
-      printedLines += 2;
-    // Lines are identical
-    } else {
-      res += other;
-      other = '';
-      if (cur === 1 || i === 0) {
-        res += `\n  ${actualLines[i]}`;
-        printedLines++;
       }
     }
     // Inspected object to big (Show ~20 rows max)
diff --git a/test/parallel/test-assert-deep.js b/test/parallel/test-assert-deep.js
index 306e8367d4..3a5fca74d4 100644
--- a/test/parallel/test-assert-deep.js
+++ b/test/parallel/test-assert-deep.js
@@ -65,9 +65,13 @@ assert.deepEqual(arr, buf);
     () => assert.deepStrictEqual(buf2, buf),
     {
       code: 'ERR_ASSERTION',
-      message: `${defaultMsgStartFull}\n\n` +
-               '  Buffer [Uint8Array] [\n    120,\n    121,\n    122,\n' +
-               '+   10,\n+   prop: 1\n-   10\n  ]'
+      message: `${defaultMsgStartFull} ... Lines skipped\n\n` +
+               '  Buffer [Uint8Array] [\n' +
+               '    120,\n' +
+               '...\n' +
+               '    10,\n' +
+               '+   prop: 1\n' +
+               '  ]'
     }
   );
   assert.deepEqual(buf2, buf);
@@ -80,9 +84,13 @@ assert.deepEqual(arr, buf);
     () => assert.deepStrictEqual(arr, arr2),
     {
       code: 'ERR_ASSERTION',
-      message: `${defaultMsgStartFull}\n\n` +
-               '  Uint8Array [\n    120,\n    121,\n    122,\n' +
-               '+   10\n-   10,\n-   prop: 5\n  ]'
+      message: `${defaultMsgStartFull} ... Lines skipped\n\n` +
+               '  Uint8Array [\n' +
+               '    120,\n' +
+               '...\n' +
+               '    10,\n' +
+               '-   prop: 5\n' +
+               '  ]'
     }
   );
   assert.deepEqual(arr, arr2);
@@ -822,7 +830,7 @@ assert.throws(
     code: 'ERR_ASSERTION',
     name: 'AssertionError [ERR_ASSERTION]',
     message: `${defaultMsgStartFull}\n\n  ` +
-             '{\n+   a: 4\n-   a: 4,\n-   b: true\n  }'
+             '{\n    a: 4,\n-   b: true\n  }'
   });
 assert.throws(
   () => assert.deepStrictEqual(['a'], { 0: 'a' }),
@@ -891,7 +899,7 @@ assert.deepStrictEqual(obj1, obj2);
   assert.throws(
     () => assert.deepStrictEqual(arrProxy, [1, 2, 3]),
     { message: `${defaultMsgStartFull}\n\n` +
-               '  [\n    1,\n+   2\n-   2,\n-   3\n  ]' }
+               '  [\n    1,\n    2,\n-   3\n  ]' }
   );
   util.inspect.defaultOptions = tmp;