Use implicit strategy when docker.host configuration is set (#4175)

core/src/main/java/org/testcontainers/utility/TestcontainersConfiguration.java

@@ -13,6 +13,7 @@
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.testcontainers.UnstableAPI;
+import org.testcontainers.dockerclient.EnvironmentAndSystemPropertyClientProviderStrategy;
 
 import java.io.File;
 import java.io.FileNotFoundException;
@@ -23,6 +24,7 @@
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.Properties;
 import java.util.concurrent.atomic.AtomicReference;
@@ -172,7 +174,27 @@ public String getDockerClientStrategyClassName() {
         // Because of this overlap, and the desire to not change this specific TESTCONTAINERS_DOCKER_CLIENT_STRATEGY setting,
         // we special-case the logic here so that docker.client.strategy is used when reading properties files and
         // TESTCONTAINERS_DOCKER_CLIENT_STRATEGY is used when searching environment variables.
-        return getEnvVarOrUserProperty("docker.client.strategy", environment.get("TESTCONTAINERS_DOCKER_CLIENT_STRATEGY"));
+
+        // looks for TESTCONTAINERS_ prefixed env var only
+        String prefixedEnvVarStrategy = environment.get("TESTCONTAINERS_DOCKER_CLIENT_STRATEGY");
+        if (prefixedEnvVarStrategy != null) {
+            return prefixedEnvVarStrategy;
+        }
+
+        // looks for unprefixed env var or unprefixed property
+        String unprefixedEnvVarOrProperty = getEnvVarOrUserProperty("docker.client.strategy", null);
+        if (unprefixedEnvVarOrProperty != null) {
+            return unprefixedEnvVarOrProperty;
+        }
+
+        // If docker.host is set then EnvironmentAndSystemPropertyClientProviderStrategy is likely to work
+        String dockerHostProperty = getEnvVarOrUserProperty("docker.host", null);
+        if (dockerHostProperty != null) {
+            return EnvironmentAndSystemPropertyClientProviderStrategy.class.getCanonicalName();
+        }
+
+        // No value set, and no implicit value to use either
+        return null;
     }
 
     public String getTransportType() {

core/src/test/java/org/testcontainers/utility/TestcontainersConfigurationTest.java

@@ -2,6 +2,7 @@
 
 import org.junit.Before;
 import org.junit.Test;
+import org.testcontainers.dockerclient.EnvironmentAndSystemPropertyClientProviderStrategy;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -155,6 +156,34 @@ public void shouldReadDockerClientStrategyFromEnvironment() {
         assertEquals("Docker client strategy is changed by env var", "foo", newConfig().getDockerClientStrategyClassName());
     }
 
+    @Test
+    public void shouldUseImplicitDockerClientStrategyWhenDockerHostPropertyIsSet() {
+        userProperties.remove("docker.client.strategy");
+        userProperties.put("docker.host", "tcp://1.2.3.4:5678");
+        assertEquals("Docker client strategy is implicitly set when docker host property is set", EnvironmentAndSystemPropertyClientProviderStrategy.class.getCanonicalName(), newConfig().getDockerClientStrategyClassName());
+    }
+
+    @Test
+    public void shouldNotUseImplicitDockerClientStrategyWhenDockerHostAndStrategyAreBothSet() {
+        userProperties.put("docker.client.strategy", "foo");
+        userProperties.put("docker.host", "tcp://1.2.3.4:5678");
+        assertEquals("Docker client strategy is can be explicitly set", "foo", newConfig().getDockerClientStrategyClassName());
+
+        userProperties.remove("docker.client.strategy");
+
+        environment.put("TESTCONTAINERS_DOCKER_CLIENT_STRATEGY", "bar");
+        userProperties.put("docker.client.strategy", "foo");
+        assertEquals("Docker client strategy is can be explicitly set", "bar", newConfig().getDockerClientStrategyClassName());
+
+        environment.put("TESTCONTAINERS_DOCKER_CLIENT_STRATEGY", "bar");
+        userProperties.remove("docker.client.strategy");
+        assertEquals("Docker client strategy is can be explicitly set", "bar", newConfig().getDockerClientStrategyClassName());
+
+        environment.remove("TESTCONTAINERS_DOCKER_CLIENT_STRATEGY");
+        userProperties.put("docker.client.strategy", "foo");
+        assertEquals("Docker client strategy is can be explicitly set", "foo", newConfig().getDockerClientStrategyClassName());
+    }
+
     @Test
     public void shouldNotReadReuseFromClasspathProperties() {
         assertFalse("no reuse by default", newConfig().environmentSupportsReuse());