Extend named-container test coverage

Adds two test additions on top of the named-lookup implementation:

- NamedContainerTest: a third field reusing an existing name, asserting
  that two fields with the same @TestContainer(name) resolve to the same
  instance.
- TestcontainerRegistryTest: plain-JUnit unit tests exercising the
  registry's lookup semantics directly — same-name same-instance via
  lookupOrCreate, lookup of an unknown name, and lookup of the empty
  string against a registry holding only named containers.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: haster

src/test/java/org/arquillian/testcontainers/NamedContainerTest.java

@@ -33,6 +33,9 @@ public static JavaArchive createDeployment() {
     @Testcontainer(name = "first")
     private SimpleTestContainer first;
 
+    @Testcontainer(name = "first")
+    private SimpleTestContainer firstAgain;
+
     @Testcontainer(name = "second")
     private SimpleTestContainer second;
 
@@ -59,4 +62,9 @@ public void checkAllDifferentInstances() {
         Assertions.assertNotSame(first, unnamed, "Expected named and unnamed containers to be different instances.");
         Assertions.assertNotSame(second, unnamed, "Expected named and unnamed containers to be different instances.");
     }
+
+    @Test
+    public void sameNameYieldsSameInstance() {
+        Assertions.assertSame(first, firstAgain, "Fields sharing a name must resolve to the same instance.");
+    }
 }

src/test/java/org/arquillian/testcontainers/TestcontainerRegistryTest.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright The Arquillian Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.arquillian.testcontainers;
+
+import java.lang.reflect.Field;
+import java.util.List;
+
+import org.arquillian.testcontainers.api.Testcontainer;
+import org.arquillian.testcontainers.common.SimpleTestContainer;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.testcontainers.containers.GenericContainer;
+
+/**
+ * Plain-JUnit unit tests for {@link TestcontainerRegistry} that exercise lookup semantics without
+ * starting any Docker containers. Annotation instances are obtained by reading the annotations off
+ * fixture fields on this class so the registry can be driven through {@code lookupOrCreate}
+ * outside an Arquillian context.
+ */
+public class TestcontainerRegistryTest {
+
+    @Testcontainer(name = "alpha")
+    private SimpleTestContainer alphaFixture;
+
+    @Test
+    public void sameNameViaLookupOrCreateReturnsSameInstance() throws Exception {
+        TestcontainerRegistry registry = new TestcontainerRegistry();
+        GenericContainer<?> first = registry.lookupOrCreate(simpleType(), annotation("alphaFixture"), List.of());
+        GenericContainer<?> second = registry.lookupOrCreate(simpleType(), annotation("alphaFixture"), List.of());
+
+        Assertions.assertSame(first, second);
+    }
+
+    @Test
+    public void lookupReturnsNullForUnknownName() throws Exception {
+        TestcontainerRegistry registry = new TestcontainerRegistry();
+        registry.lookupOrCreate(simpleType(), annotation("alphaFixture"), List.of());
+
+        Assertions.assertNull(registry.lookup("missing"));
+    }
+
+    @Test
+    public void emptyNameLookupDoesNotMatchNamedContainers() throws Exception {
+        TestcontainerRegistry registry = new TestcontainerRegistry();
+        registry.lookupOrCreate(simpleType(), annotation("alphaFixture"), List.of());
+
+        Assertions.assertNull(registry.lookup(""),
+                "Empty-string lookup should not return any registered container");
+    }
+
+    @SuppressWarnings("unchecked")
+    private static Class<GenericContainer<?>> simpleType() {
+        return (Class<GenericContainer<?>>) (Class<?>) SimpleTestContainer.class;
+    }
+
+    private Testcontainer annotation(final String fieldName) throws NoSuchFieldException {
+        final Field field = TestcontainerRegistryTest.class.getDeclaredField(fieldName);
+        return field.getAnnotation(Testcontainer.class);
+    }
+}