when:
        def result = cache.get(file)

        then:
        result == 12

        and:
        1 * fileSystemAccess.readRegularFileContentHash(file.absolutePath) >> Optional.empty()
        1 * calculator.calculate(file, false) >> 12
        0 * _

        when:
        result = cache.get(file)

        then:
        result == 12

    /**
     * Visits the hash of the content of the file only if the file is a regular file.
     *
     * @return the visitor function applied to the found snapshot.
     */
    Optional<HashCode> readRegularFileContentHash(String location);

    /**
     * Reads the hierarchy of files at the given location.
     */
    FileSystemLocationSnapshot read(String location);

    /**

            locationCache.clear();
        }

        @Override
        public V get(File file) {
            return locationCache.computeIfAbsent(file,
                location -> fileSystemAccess.readRegularFileContentHash(location.getAbsolutePath())
                    .map(contentHash -> contentCache.get(contentHash, key -> calculator.calculate(location, true))
                ).orElseGet(