calledWith(f, s);
    }

    void check() {
      runTester();
      NullRejectingFromTo<?, ?> defaultFunction =
          (NullRejectingFromTo<?, ?>) getDefaultParameterValue(0);
      assertNotNull(defaultFunction);
      try {
        defaultFunction.apply(null);
        fail("Proxy Should have rejected null");
      } catch (NullPointerException expected) {
      }
    }
  }

    private final static int DEFAULT_RETENTION_PERIOD_DAYS = 7

    def operations = new BuildOperationsFixture(executer, testDirectoryProvider)
    def hashStringLength = Hashing.defaultFunction().hexDigits

    abstract String getBuildCacheName();
    abstract void createBuildCacheEntry(String key, File value, long timestamp);
    abstract boolean existsBuildCacheEntry(String key);

        Hasher hasher = newHasher();
        hasher.put(hashable);
        return hasher.hash();
    }

    /**
     * The default hashing function.
     */
    public static HashFunction defaultFunction() {
        return DEFAULT;
    }

    /**
     * MD5 hashing function.
     */
    public static HashFunction md5() {
        return MD5;
    }

    /**