assert: make skipping indicator blue

If lines gets skipped, they are marked with three dots. This makes
sure they are better visualized to distinguish them from everything
else.

PR-URL: nodejs#20315
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

lib/internal/errors.js

@@ -15,6 +15,7 @@ const kInfo = Symbol('info');
 const messages = new Map();
 const codes = {};
 
+let blue = '';
 let green = '';
 let red = '';
 let white = '';
@@ -259,7 +260,7 @@ function createErrDiff(actual, expected, operator) {
   const expectedLines = inspectValue(expected);
   const msg = READABLE_OPERATOR[operator] +
         `:\n${green}+ expected${white} ${red}- actual${white}`;
-  const skippedMsg = ' ... Lines skipped';
+  const skippedMsg = ` ${blue}...${white} Lines skipped`;
 
   // Remove all ending lines that match (this optimizes the output for
   // readability by reducing the number of total changed lines).
@@ -280,7 +281,7 @@ function createErrDiff(actual, expected, operator) {
     b = expectedLines[expectedLines.length - 1];
   }
   if (i > 3) {
-    end = `\n...${end}`;
+    end = `\n${blue}...${white}${end}`;
     skipped = true;
   }
   if (other !== '') {
@@ -297,7 +298,7 @@ function createErrDiff(actual, expected, operator) {
     if (actualLines.length < i + 1) {
       if (cur > 1 && i > 2) {
         if (cur > 4) {
-          res += '\n...';
+          res += `\n${blue}...${white}`;
           skipped = true;
         } else if (cur > 3) {
           res += `\n  ${expectedLines[i - 2]}`;
@@ -313,7 +314,7 @@ function createErrDiff(actual, expected, operator) {
     } else if (expectedLines.length < i + 1) {
       if (cur > 1 && i > 2) {
         if (cur > 4) {
-          res += '\n...';
+          res += `\n${blue}...${white}`;
           skipped = true;
         } else if (cur > 3) {
           res += `\n  ${actualLines[i - 2]}`;
@@ -329,7 +330,7 @@ function createErrDiff(actual, expected, operator) {
     } else if (actualLines[i] !== expectedLines[i]) {
       if (cur > 1 && i > 2) {
         if (cur > 4) {
-          res += '\n...';
+          res += `\n${blue}...${white}`;
           skipped = true;
         } else if (cur > 3) {
           res += `\n  ${actualLines[i - 2]}`;
@@ -354,7 +355,8 @@ function createErrDiff(actual, expected, operator) {
     }
     // Inspected object to big (Show ~20 rows max)
     if (printedLines > 20 && i < maxLines - 2) {
-      return `${msg}${skippedMsg}\n${res}\n...${other}\n...`;
+      return `${msg}${skippedMsg}\n${res}\n${blue}...${white}${other}\n` +
+        `${blue}...${white}`;
     }
   }
 
@@ -371,7 +373,7 @@ function createErrDiff(actual, expected, operator) {
     // Only remove lines in case it makes sense to collapse those.
     // TODO: Accept env to always show the full error.
     if (actualLines.length > 30) {
-      actualLines[26] = '...';
+      actualLines[26] = `${blue}...${white}`;
       while (actualLines.length > 27) {
         actualLines.pop();
       }
@@ -402,10 +404,12 @@ class AssertionError extends Error {
         // Reset on each call to make sure we handle dynamically set environment
         // variables correct.
         if (process.stdout.getColorDepth() !== 1) {
+          blue = '\u001b[34m';
           green = '\u001b[32m';
           white = '\u001b[39m';
           red = '\u001b[31m';
         } else {
+          blue = '';
           green = '';
           white = '';
           red = '';
@@ -435,7 +439,7 @@ class AssertionError extends Error {
         // Only remove lines in case it makes sense to collapse those.
         // TODO: Accept env to always show the full error.
         if (res.length > 30) {
-          res[26] = '...';
+          res[26] = `${blue}...${white}`;
           while (res.length > 27) {
             res.pop();
           }

test/pseudo-tty/test-assert-colors.js

@@ -5,13 +5,16 @@ const assert = require('assert').strict;
 try {
   // Activate colors even if the tty does not support colors.
   process.env.COLORTERM = '1';
-  assert.deepStrictEqual([1, 2], [2, 2]);
+  assert.deepStrictEqual([1, 2, 2, 2], [2, 2, 2, 2]);
 } catch (err) {
   const expected = 'Input A expected to strictly deep-equal input B:\n' +
-    '\u001b[32m+ expected\u001b[39m \u001b[31m- actual\u001b[39m\n\n' +
+    '\u001b[32m+ expected\u001b[39m \u001b[31m- actual\u001b[39m' +
+      ' \u001b[34m...\u001b[39m Lines skipped\n\n' +
     '  [\n' +
     '\u001b[31m-\u001b[39m   1,\n' +
     '\u001b[32m+\u001b[39m   2,\n' +
+    '    2,\n' +
+    '\u001b[34m...\u001b[39m\n' +
     '    2\n' +
     '  ]';
   assert.strictEqual(err.message, expected);