@Test
    public void testWhenConfigAbsent() {
        Mockito
            .doReturn("auto")
            .when(TestcontainersConfiguration.getInstance())
            .getEnvVarOrProperty(eq("dockerconfig.source"), anyString());
        Mockito
            .doReturn(null)
            .when(TestcontainersConfiguration.getInstance())
            .getEnvVarOrUserProperty(eq("docker.host"), isNull());
        Mockito
            .doReturn(null)
            .when(TestcontainersConfiguration.getInstance())
            .getEnvVarOrUserProperty(eq("docker.tls.verify"), isNull());
        Mockito
            .doReturn(null)
            .when(TestcontainersConfiguration.getInstance())
            .getEnvVarOrUserProperty(eq("docker.cert.path"), isNull());

        EnvironmentAndSystemPropertyClientProviderStrategy strategy = new EnvironmentAndSystemPropertyClientProviderStrategy();

        TransportConfig transportConfig = strategy.getTransportConfig();
        assertThat(transportConfig.getDockerHost()).isEqualTo(defaultDockerHost);
        assertThat(transportConfig.getSslConfig()).isEqualTo(defaultSSLConfig);
    }
Test that we can use Testcontainers configuration file to override settings. We assume that docker-java has test
coverage for detection of environment variables (e.g. DOCKER_HOST) and its own properties config file.
core/src/test/java/org/testcontainers/dockerclient/EnvironmentAndSystemPropertyClientProviderStrategyTest.java