public String getEmulatorGrpcEndpoint() {
        return getHost() + ":" + getMappedPort(GRPC_PORT);
    }
@return a <code>host:port</code> pair corresponding to the address on which the emulator's
gRPC endpoint is reachable from the test host machine. Directly usable as a parameter to the
com.google.cloud.spanner.SpannerOptions.Builder#setEmulatorHost(java.lang.String) method.
modules/gcloud/src/main/java/org/testcontainers/containers/SpannerEmulatorContainer.java