@SuppressWarnings("unchecked") // `R` and `A` match for an `IDENTITY_FINISH`
        R result = (R) finalAccum;
        assertEquivalent(expectedResult, result);
      }
      assertEquivalent(expectedResult, collector.finisher().apply(finalAccum));
    }
  }

  private void assertEquivalent(R expected, R actual) {
    assertTrue(
        "Expected " + expected + " got " + actual + " modulo equivalence " + equivalence,