assertEquals(4, algNames.size());
    }

    @Test
    void emptySha1Calculator() {
        ChecksumAlgorithmService.ChecksumCalculator calculator =
                service.select("SHA-1").getCalculator();
        calculator.update(ByteBuffer.allocate(0));
        assertEquals(calculator.checksum(), "da39a3ee5e6b4b0d3255bfef95601890afd80709");
    }

    @Test
    void calculateByte() throws IOException {

        @Nonnull
        String getFileExtension();

        /**
         * Each invocation of this method returns a new instance of calculator, never {@code null} value.
         */
        @Nonnull
        ChecksumCalculator getCalculator();
    }

    /**
     * The checksum calculator.
     */
    interface ChecksumCalculator {
        /**
         * Updates the checksum algorithm inner state with input.