testObjectWithSymbolKeys() {
      const s = Symbol(5);
      const a = {};
      a[s] = 'hello world';
      const f = deepFreeze(a);
      assertEquals('hello world', f[s]);
      // The below check would be an assertThrows, but the Symbol polyfill for
      // IE doesn't throw when changing a frozen symbol key's value.
      try {
        f[s] = 'new thing!';
      } catch (expectedInStrictMode) {
      }
      assertEquals('hello world', f[s]);
      assertThrows(() => {
        console.log(a[s]);
      });
    }
@suppress {missingProperties} suppression added to enable type
checking