fix(cdk/testing): fix value stringification in harnesses (#23421)

* fix(cdk/testing): fix value stringification in harnesses

* fixup! fix(cdk/testing): fix value stringification in harnesses

(cherry picked from commit 829e095)

Author: mmalerba

src/cdk/testing/component-harness.ts

@@ -561,15 +561,18 @@ function _valueAsString(value: unknown) {
   if (value === undefined) {
     return 'undefined';
   }
-  // `JSON.stringify` doesn't handle RegExp properly, so we need a custom replacer.
   try {
-    return JSON.stringify(value, (_, v) => {
-      if (v instanceof RegExp) {
-        return `/${v.toString()}/`;
-      }
-
-      return typeof v === 'string' ? v.replace('/\//g', '\\/') : v;
-    }).replace(/"\/\//g, '\\/').replace(/\/\/"/g, '\\/').replace(/\\\//g, '/');
+    // `JSON.stringify` doesn't handle RegExp properly, so we need a custom replacer.
+    // Use a character that is unlikely to appear in real strings to denote the start and end of
+    // the regex. This allows us to strip out the extra quotes around the value added by
+    // `JSON.stringify`. Also do custom escaping on `"` characters to prevent `JSON.stringify`
+    // from escaping them as if they were part of a string.
+    const stringifiedValue = JSON.stringify(value, (_, v) => v instanceof RegExp ?
+        `◬MAT_RE_ESCAPE◬${v.toString().replace(/"/g, '◬MAT_RE_ESCAPE◬')}◬MAT_RE_ESCAPE◬` : v);
+    // Strip out the extra quotes around regexes and put back the manually escaped `"` characters.
+    return stringifiedValue
+        .replace(/"◬MAT_RE_ESCAPE◬|◬MAT_RE_ESCAPE◬"/g, '')
+        .replace(/◬MAT_RE_ESCAPE◬/g, '"');
   } catch {
     // `JSON.stringify` will throw if the object is cyclical,
     // in this case the best we can do is report the value as `{...}`.

src/cdk/testing/tests/cross-environment.spec.ts

@@ -9,7 +9,7 @@
 import {
   ComponentHarness,
   ComponentHarnessConstructor,
-  HarnessLoader,
+  HarnessLoader, HarnessPredicate,
   parallel,
   TestElement,
 } from '@angular/cdk/testing';
@@ -311,6 +311,19 @@ export function crossEnvironmentSpecs(
             ' the constraints: title = "List of test tools", item count = 4)');
       }
     });
+
+    it('should have correct description for debugging', () => {
+      const predicate = new HarnessPredicate(MainComponentHarness, {})
+          .addOption('test', {
+            regexes: [/test/gim, /"test"/],
+            strings: [`test`, `"test"`],
+            numbers: [10]
+          }, async () => true);
+      expect(predicate.getDescription()).toBe(`test = {` +
+          `"regexes":[/test/gim,/"test"/],` +
+          `"strings":["test","\\"test\\""],` +
+          `"numbers":[10]}`);
+    });
   });
 
   describe('TestElement', () => {