assert: improve the strict equal messages

lib/internal/assert.js

@@ -11,15 +11,18 @@ let red = '';
 let white = '';
 
 const kReadableOperator = {
-  deepStrictEqual: 'Expected inputs to be strictly deep-equal:',
-  strictEqual: 'Expected inputs to be strictly equal:',
-  deepEqual: 'Expected inputs to be loosely deep-equal:',
-  equal: 'Expected inputs to be loosely equal:',
+  deepStrictEqual: 'Expected values to be strictly deep-equal:',
+  strictEqual: 'Expected values to be strictly equal:',
+  strictEqualObject: 'Expected "actual" to be reference-equal to "expected":',
+  deepEqual: 'Expected values to be loosely deep-equal:',
+  equal: 'Expected values to be loosely equal:',
   notDeepStrictEqual: 'Expected "actual" not to be strictly deep-equal to:',
   notStrictEqual: 'Expected "actual" to be strictly unequal to:',
+  // eslint-disable-next-line max-len
+  notStrictEqualObject: 'Expected "actual" not to be reference-equal to "expected":',
   notDeepEqual: 'Expected "actual" not to be loosely deep-equal to:',
   notEqual: 'Expected "actual" to be loosely unequal to:',
-  notIdentical: 'Inputs identical but not reference equal:',
+  notIdentical: 'Values identical but not reference-equal:',
 };
 
 // Comparing short primitives should just show === / !== instead of using the
@@ -67,13 +70,20 @@ function createErrDiff(actual, expected, operator) {
   const actualInspected = inspectValue(actual);
   const actualLines = actualInspected.split('\n');
   const expectedLines = inspectValue(expected).split('\n');
-  const msg = kReadableOperator[operator] +
-        `\n${green}+ actual${white} ${red}- expected${white}`;
-  const skippedMsg = ` ${blue}...${white} Lines skipped`;
 
   let i = 0;
   let indicator = '';
 
+  // In case both values are objects explicitly mark them as not reference equal
+  // for the `strictEqual` operator.
+  if (operator === 'strictEqual' &&
+      typeof actual === 'object' &&
+      typeof expected === 'object' &&
+      actual !== null &&
+      expected !== null) {
+    operator = 'strictEqualObject';
+  }
+
   // If "actual" and "expected" fit on a single line and they are not strictly
   // equal, check further special handling.
   if (actualLines.length === 1 && expectedLines.length === 1 &&
@@ -89,7 +99,7 @@ function createErrDiff(actual, expected, operator) {
         return `${kReadableOperator[operator]}\n\n` +
             `${actualLines[0]} !== ${expectedLines[0]}\n`;
       }
-    } else {
+    } else if (operator !== 'strictEqualObject') {
       // If the stderr is a tty and the input length is lower than the current
       // columns per line, add a mismatch indicator below the output. If it is
       // not a tty, use a default value of 80 characters.
@@ -156,6 +166,10 @@ function createErrDiff(actual, expected, operator) {
   }
 
   let printedLines = 0;
+  const msg = kReadableOperator[operator] +
+        `\n${green}+ actual${white} ${red}- expected${white}`;
+  const skippedMsg = ` ${blue}...${white} Lines skipped`;
+
   for (i = 0; i < maxLines; i++) {
     // Only extra expected lines exist
     const cur = i - lastPos;
@@ -274,8 +288,15 @@ class AssertionError extends Error {
         operator === 'notStrictEqual') {
         // In case the objects are equal but the operator requires unequal, show
         // the first object and say A equals B
+        let base = kReadableOperator[operator];
         const res = inspectValue(actual).split('\n');
-        const base = kReadableOperator[operator];
+
+        // In case "actual" is an object, it should not be reference equal.
+        if (operator === 'notStrictEqual' &&
+            typeof actual === 'object' &&
+            actual !== null) {
+          base = kReadableOperator.notStrictEqualObject;
+        }
 
         // Only remove lines in case it makes sense to collapse those.
         // TODO: Accept env to always show the full error.

test/message/assert_throws_stack.out

@@ -2,7 +2,7 @@ assert.js:*
       throw err;
       ^
 
-AssertionError [ERR_ASSERTION]: Expected inputs to be strictly deep-equal:
+AssertionError [ERR_ASSERTION]: Expected values to be strictly deep-equal:
 + actual - expected
 
 + Comparison {}

test/message/error_exit.out

@@ -3,7 +3,7 @@ assert.js:*
   throw new AssertionError(obj);
   ^
 
-AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
+AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
 
 1 !== 2
 

test/parallel/test-assert-checktag.js

@@ -26,14 +26,14 @@ if (process.stdout.isTTY)
   assert.throws(
     () => assert.deepStrictEqual(date, fake),
     {
-      message: 'Expected inputs to be strictly deep-equal:\n' +
+      message: 'Expected values to be strictly deep-equal:\n' +
                '+ actual - expected\n\n+ 2016-01-01T00:00:00.000Z\n- Date {}'
     }
   );
   assert.throws(
     () => assert.deepStrictEqual(fake, date),
     {
-      message: 'Expected inputs to be strictly deep-equal:\n' +
+      message: 'Expected values to be strictly deep-equal:\n' +
                '+ actual - expected\n\n+ Date {}\n- 2016-01-01T00:00:00.000Z'
     }
   );

test/parallel/test-assert-deep.js

@@ -4,7 +4,7 @@ require('../common');
 const assert = require('assert');
 const util = require('util');
 const { AssertionError } = assert;
-const defaultMsgStart = 'Expected inputs to be strictly deep-equal:\n';
+const defaultMsgStart = 'Expected values to be strictly deep-equal:\n';
 const defaultMsgStartFull = `${defaultMsgStart}+ actual - expected`;
 
 // Disable colored output to prevent color codes from breaking assertion
@@ -16,7 +16,7 @@ if (process.stdout.isTTY)
 // Template tag function turning an error message into a RegExp
 // for assert.throws()
 function re(literals, ...values) {
-  let result = 'Expected inputs to be loosely deep-equal:\n\n';
+  let result = 'Expected values to be loosely deep-equal:\n\n';
   for (const [i, value] of values.entries()) {
     const str = util.inspect(value, {
       compact: false,

test/parallel/test-assert.js

@@ -34,8 +34,8 @@ const a = assert;
 if (process.stdout.isTTY)
   process.env.NODE_DISABLE_COLORS = '1';
 
-const strictEqualMessageStart = 'Expected inputs to be strictly equal:\n';
-const start = 'Expected inputs to be strictly deep-equal:';
+const strictEqualMessageStart = 'Expected values to be strictly equal:\n';
+const start = 'Expected values to be strictly deep-equal:';
 const actExp = '+ actual - expected';
 
 assert.ok(a.AssertionError.prototype instanceof Error,
@@ -415,9 +415,9 @@ assert.throws(
   {
     code: 'ERR_ASSERTION',
     name: 'AssertionError [ERR_ASSERTION]',
-    message: strictEqualMessageStart +
+    message: 'Expected "actual" to be reference-equal to "expected":\n' +
              '+ actual - expected\n\n' +
-             '+ [Error: foo]\n- [Error: foobar]\n             ^'
+             '+ [Error: foo]\n- [Error: foobar]'
   }
 );
 
@@ -1013,7 +1013,7 @@ assert.throws(() => { throw null; }, 'foo');
 assert.throws(
   () => assert.strictEqual([], []),
   {
-    message: 'Inputs identical but not reference equal:\n\n[]\n'
+    message: 'Values identical but not reference-equal:\n\n[]\n'
   }
 );
 
@@ -1022,7 +1022,8 @@ assert.throws(
   assert.throws(
     () => assert.strictEqual(args, { 0: 'a' }),
     {
-      message: `${strictEqualMessageStart}+ actual - expected\n\n` +
+      message: 'Expected "actual" to be reference-equal to "expected":\n' +
+               '+ actual - expected\n\n' +
                "+ [Arguments] {\n- {\n    '0': 'a'\n  }"
     }
   );
@@ -1091,3 +1092,43 @@ assert.throws(
     }
   );
 }
+
+// Indicate where the strings diverge.
+assert.throws(
+  () => assert.strictEqual('test test', 'test foobar'),
+  {
+    code: 'ERR_ASSERTION',
+    name: 'AssertionError [ERR_ASSERTION]',
+    message: strictEqualMessageStart +
+             '+ actual - expected\n\n' +
+             "+ 'test test'\n" +
+             "- 'test foobar'\n" +
+             '        ^'
+  }
+);
+
+// Check for reference-equal objects in `notStrictEqual()`
+assert.throws(
+  () => {
+    const obj = {};
+    assert.notStrictEqual(obj, obj);
+  },
+  {
+    code: 'ERR_ASSERTION',
+    name: 'AssertionError [ERR_ASSERTION]',
+    message: 'Expected "actual" not to be reference-equal to "expected": {}'
+  }
+);
+
+assert.throws(
+  () => {
+    const obj = { a: true };
+    assert.notStrictEqual(obj, obj);
+  },
+  {
+    code: 'ERR_ASSERTION',
+    name: 'AssertionError [ERR_ASSERTION]',
+    message: 'Expected "actual" not to be reference-equal to "expected":\n\n' +
+             '{\n  a: true\n}\n'
+  }
+);

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

@@ -7,7 +7,7 @@ try {
   process.env.COLORTERM = '1';
   assert.deepStrictEqual([1, 2, 2, 2], [2, 2, 2, 2]);
 } catch (err) {
-  const expected = 'Expected inputs to be strictly deep-equal:\n' +
+  const expected = 'Expected values to be strictly deep-equal:\n' +
     '\u001b[32m+ actual\u001b[39m \u001b[31m- expected\u001b[39m' +
       ' \u001b[34m...\u001b[39m Lines skipped\n\n' +
     '  [\n' +