@VisibleForTesting
    Optional<String> findContainerForReuse(String hash) {
        // TODO locking
        return dockerClient
            .listContainersCmd()
            .withLabelFilter(ImmutableMap.of(HASH_LABEL, hash))
            .withLimit(1)
            .withStatusFilter(Arrays.asList("running"))
            .exec()
            .stream()
            .findAny()
            .map(it -> it.getId());
    }
Starts the container using docker, pulling an image if necessary.
core/src/main/java/org/testcontainers/containers/GenericContainer.java