Add IT for SpEL topics on @PulsarMessage

This commit adds a lightweight integration test nested in the
DefaultTopicResolverTests which uses a small Spring context to verify
actual expression evaluation.

See #568

spring-pulsar/src/main/java/org/springframework/pulsar/core/DefaultExpressionResolver.java

@@ -25,6 +25,7 @@ import org.springframework.beans.factory.config.ConfigurableBeanFactory;
  * {@link ConfigurableBeanFactory} capabilities to resolve expressions.
  *
  * @author Jonas Geiregat
+ * @since 1.1.0
  */
 public class DefaultExpressionResolver implements ExpressionResolver {
 
@@ -40,6 +41,13 @@ public class DefaultExpressionResolver implements ExpressionResolver {
 		this.configurableBeanFactory = configurableBeanFactory;
 	}
 
+	/**
+	 * {@inheritDoc}
+	 * @param expression the expression to resolve (can include property placeholders and
+	 * SpEL)
+	 * @return a {@code Resolved} instance containing the resolved string value (can be
+	 * null) or an exception if the resolution failed.
+	 */
 	@Override
 	public Resolved<String> resolveToString(String expression) {
 		String placeholdersResolved = this.configurableBeanFactory.resolveEmbeddedValue(expression);
@@ -51,7 +59,7 @@ public class DefaultExpressionResolver implements ExpressionResolver {
 			return Resolved.of(null);
 		}
 		return Resolved
-				.failed("The expression '%s' must resolve to a string but was: %s".formatted(expression, resolvedObj));
+			.failed("The expression '%s' must resolve to a string but was: %s".formatted(expression, resolvedObj));
 	}
 
 }

spring-pulsar/src/main/java/org/springframework/pulsar/core/ExpressionResolver.java

@@ -17,16 +17,18 @@
 package org.springframework.pulsar.core;
 
 /**
- * Resolves expressions.
+ * Strategy interface for resolving a value from a string expression.
  *
  * @author Jonas Geiregat
+ * @since 1.1.0
  */
 public interface ExpressionResolver {
 
 	/**
-	 * Resolve the given expression.
+	 * Resolve the given expression as a string value.
 	 * @param expression the expression to resolve
-	 * @return the resolved value as a {@code Resolved} of {@link String}
+	 * @return a {@code Resolved} instance containing the resolved string value (can be
+	 * null) or an exception if the resolution failed.
 	 */
 	Resolved<String> resolveToString(String expression);
 

spring-pulsar/src/test/java/org/springframework/pulsar/core/DefaultTopicResolverTests.java

@@ -18,11 +18,9 @@ package org.springframework.pulsar.core;
 
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 import static org.junit.jupiter.params.provider.Arguments.arguments;
-import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.when;
 
 import java.util.stream.Stream;
 
@@ -35,9 +33,17 @@ import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 
-import org.springframework.beans.factory.config.ConfigurableBeanFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
 import org.springframework.lang.Nullable;
 import org.springframework.pulsar.annotation.PulsarMessage;
+import org.springframework.pulsar.core.DefaultTopicResolverTests.TopicByAnnotatedMessageType.WithTopicExpression.WithTopicExpressionConfig;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.annotation.DirtiesContext.ClassMode;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 
 /**
  * Unit tests for {@link DefaultTopicResolver}.
@@ -138,8 +144,6 @@ class DefaultTopicResolverTests {
 	@Nested
 	class TopicByAnnotatedMessageType {
 
-		private static final String bazTopicExpression = "#{someExpression}";
-
 		@Test
 		void customMappingTakesPrecedenceOverAnnotationMapping() {
 			assertThat(resolver.resolveTopic(null, Baz.class, () -> defaultTopic).value().orElse(null))
@@ -169,29 +173,63 @@ class DefaultTopicResolverTests {
 			verify(resolver, times(1)).getAnnotatedTopicInfo(Baz.class);
 		}
 
-		@Test
-		void annotatedMessageTypeWithTopicExpressionIsResolved() {
-			var mockExpressionResolver = mock(ExpressionResolver.class);
-			when(mockExpressionResolver.resolveToString(bazTopicExpression)).thenReturn(Resolved.of(bazTopic));
-			var expressionTopicResolver = new DefaultTopicResolver(mockExpressionResolver);
-			assertThat(expressionTopicResolver.resolveTopic(null, BazWithTopicExpression.class,
-					() -> defaultTopic).value().orElse(null))
-					.isEqualTo(bazTopic);
-			verify(mockExpressionResolver, times(1)).resolveToString(bazTopicExpression);
-		}
+		/**
+		 * Lightweight integration tests for the expression resolver functionality in
+		 * {@link DefaultTopicResolver}.
+		 * <p>
+		 * Starts up a small Spring context which in turns provides the bean factory and
+		 * expression resolver to the topic resolver.
+		 */
+		@Nested
+		@SpringJUnitConfig
+		@DirtiesContext(classMode = ClassMode.AFTER_CLASS)
+		@ContextConfiguration(classes = WithTopicExpressionConfig.class)
+		@TestPropertySource(properties = { "app.customPropertyTopic = my-custom-property-topic" })
+		class WithTopicExpression {
 
-		@Test
-		void deriveExpressionResolverFromBeanFactory() {
-			var mockBeanFactory = mock(ConfigurableBeanFactory.class);
-			var expressionTopicResolver = new DefaultTopicResolver();
-			expressionTopicResolver.setBeanFactory(mockBeanFactory);
-			assertThat(expressionTopicResolver)
-					.extracting("expressionResolver")
-					.isNotNull();
-		}
+			// @formatter:off
+			@Test
+			void propertyPlaceholderExpressionIsResolved(@Autowired DefaultTopicResolver topicResolver) {
+				assertThat(topicResolver.resolveTopic(null, MsgTypeWithTopicPropertyExpression.class, () -> defaultTopic)
+							.value().orElse(null)).isEqualTo("my-custom-property-topic");
+
+			}
+
+			@Test
+			void spelExpressionIsResolved(@Autowired DefaultTopicResolver topicResolver) {
+				assertThat(topicResolver.resolveTopic(null, MsgTypeWithTopicSpELExpression.class, () -> defaultTopic)
+					.value().orElse(null)).isEqualTo("my-custom-spel-topic");
+			}
+
+			@Test
+			void embeddedExpressionIsResolved(@Autowired DefaultTopicResolver topicResolver) {
+				assertThat(topicResolver.resolveTopic(null, MsgTypeWithTopicEmbeddedExpression.class, () -> defaultTopic)
+							.value().orElse(null)).isEqualTo("my-custom-property-topic".toUpperCase());
+			}
+			// @formatter:on
+
+			@Configuration(proxyBeanMethods = false)
+			static class WithTopicExpressionConfig {
+
+				@Bean
+				DefaultTopicResolver defaultTopicResolver() {
+					return new DefaultTopicResolver();
+				}
+
+			}
+
+			@PulsarMessage(topic = "${app.customPropertyTopic}")
+			record MsgTypeWithTopicPropertyExpression(String value) {
+			}
+
+			@PulsarMessage(topic = "#{T(java.lang.String).valueOf('my-custom-spel-topic')}")
+			record MsgTypeWithTopicSpELExpression(String value) {
+			}
+
+			@PulsarMessage(topic = "#{T(java.lang.String).valueOf('${app.customPropertyTopic}').toUpperCase()}")
+			record MsgTypeWithTopicEmbeddedExpression(String value) {
+			}
 
-		@PulsarMessage(topic = bazTopicExpression)
-		record BazWithTopicExpression(String value) {
 		}
 
 	}