assert: make actual and expected getters

The `actual` and `expected` properties on an instance of
`AssertionError` is now a getter to prevent inspecting these when
inspecting the error. These values will be visible in the error
message and showing them otherwise would decrease the readability
of the error.

PR-URL: #25250
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>

lib/internal/assert.js

@@ -395,6 +395,14 @@ class AssertionError extends Error {
     this.operator = operator;
     Error.captureStackTrace(this, stackStartFn);
   }
+
+  [inspect.custom](recurseTimes, ctx) {
+    // This limits the `actual` and `expected` property default inspection to
+    // the minimum depth. Otherwise those values would be too verbose compared
+    // to the actual error message which contains a combined view of these two
+    // input values.
+    return inspect(this, { ...ctx, customInspect: false, depth: 0 });
+  }
 }
 
 module.exports = {

test/parallel/test-assert.js

@@ -1139,3 +1139,14 @@ assert.throws(
              '{\n  a: true\n}\n'
   }
 );
+
+{
+  let threw = false;
+  try {
+    assert.deepStrictEqual(Array(100).fill(1), 'foobar');
+  } catch (err) {
+    threw = true;
+    assert(/actual: \[Array],\n  expected: 'foobar',/.test(inspect(err)));
+  }
+  assert(threw);
+}