assert: refactor AssertionError properties

lib/internal/assert.js

@@ -390,8 +390,32 @@ class AssertionError extends Error {
     this.generatedMessage = !message;
     this.name = 'AssertionError [ERR_ASSERTION]';
     this.code = 'ERR_ASSERTION';
-    this.actual = actual;
-    this.expected = expected;
+    // This prevents inspecting the actual and expected value by default.
+    // That is logical since the summary will be printed already. Users can then
+    // explicitly access these properties in case they want to know what value
+    // was used.
+    Object.defineProperties(this, {
+      actual: {
+        get() {
+          return actual;
+        },
+        set(val) {
+          actual = val;
+        },
+        enumerable: true,
+        configurable: true
+      },
+      expected: {
+        get() {
+          return expected;
+        },
+        set(val) {
+          expected = val;
+        },
+        enumerable: true,
+        configurable: true
+      }
+    });
     this.operator = operator;
     Error.captureStackTrace(this, stackStartFn);
   }

test/parallel/test-assert.js

@@ -257,16 +257,14 @@ const circular = { y: 1 };
 circular.x = circular;
 
 function testAssertionMessage(actual, expected, msg) {
-  try {
-    assert.strictEqual(actual, '');
-  } catch (e) {
-    assert.strictEqual(
-      e.message,
-      msg || strictEqualMessageStart +
-             `+ actual - expected\n\n+ ${expected}\n- ''`
-    );
-    assert.ok(e.generatedMessage, 'Message not marked as generated');
-  }
+  assert.throws(
+    () => assert.strictEqual(actual, ''),
+    {
+      generatedMessage: true,
+      message: msg || strictEqualMessageStart +
+               `+ actual - expected\n\n+ ${expected}\n- ''`
+    }
+  );
 }
 
 function testShortAssertionMessage(actual, expected) {
@@ -280,7 +278,7 @@ testShortAssertionMessage(false, 'false');
 testShortAssertionMessage(100, '100');
 testShortAssertionMessage(NaN, 'NaN');
 testShortAssertionMessage(Infinity, 'Infinity');
-testShortAssertionMessage('', '""');
+testShortAssertionMessage('a', '"a"');
 testShortAssertionMessage('foo', '\'foo\'');
 testShortAssertionMessage(0, '0');
 testShortAssertionMessage(Symbol(), 'Symbol()');
@@ -308,6 +306,16 @@ try {
     `${strictEqualMessageStart}\n1 !== 2\n`
   );
   assert.ok(e.generatedMessage, 'Message not marked as generated');
+  const descriptors = Object.getOwnPropertyDescriptors(e);
+  assert.strictEqual(typeof descriptors.actual.get, 'function');
+  assert.strictEqual(typeof descriptors.expected.get, 'function');
+  const { actual, expected } = e;
+  e.actual++;
+  e.expected++;
+  assert.strictEqual(descriptors.actual.enumerable, true);
+  assert.strictEqual(descriptors.expected.enumerable, true);
+  assert.strictEqual(e.actual, actual + 1);
+  assert.strictEqual(e.expected, expected + 1);
 }
 
 try {