public String getEmulatorHttpEndpoint() {
        return getHost() + ":" + getMappedPort(HTTP_PORT);
    }
@return a <code>host:port</code> pair corresponding to the address on which the emulator's
HTTP REST endpoint is reachable from the test host machine.
modules/gcloud/src/main/java/org/testcontainers/containers/SpannerEmulatorContainer.java