added example for multidocument properties files

spring-boot-modules/spring-boot-properties-3/src/main/resources/application.properties

@@ -8,4 +8,8 @@ spring.datasource.url=jdbc:h2:dev
 spring.datasource.username=SA
 spring.datasource.password=password
 app.name=MyApp
-app.description=${app.name} is a Spring Boot application
+app.description=${app.name} is a Spring Boot application
+bael.property=defaultValue
+#---
+spring.config.activate.on-profile=prod
+bael.property=prodValue

spring-boot-modules/spring-boot-properties-3/src/test/java/com/baeldung/boot/properties/multidocument/DefaultMultidocumentPropertiesFileIntegrationTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.boot.properties.multidocument;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+
+import com.baeldung.boot.properties.DemoApplication;
+
+@SpringBootTest(classes = { DemoApplication.class }, webEnvironment = WebEnvironment.MOCK)
+public class DefaultMultidocumentPropertiesFileIntegrationTest {
+
+    @Value("${bael.property}")
+    private String baelCustomProperty;
+
+    @Test
+    public void givenDefaultProfileActive_whenApplicationStarts_thenDefaultPropertiesUser() {
+        assertThat(baelCustomProperty).isEqualTo("defaultValue");
+    }
+}

spring-boot-modules/spring-boot-properties-3/src/test/java/com/baeldung/boot/properties/multidocument/ProdMultidocumentPropertiesFileIntegrationTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.boot.properties.multidocument;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.test.context.ActiveProfiles;
+
+import com.baeldung.boot.properties.DemoApplication;
+
+@SpringBootTest(classes = { DemoApplication.class }, webEnvironment = WebEnvironment.MOCK)
+@ActiveProfiles("prod")
+public class ProdMultidocumentPropertiesFileIntegrationTest {
+
+    @Value("${bael.property}")
+    private String baelCustomProperty;
+
+    @Test
+    public void givenProductionProfileActive_whenApplicationStarts_thenDefaultPropertiesUser() {
+        assertThat(baelCustomProperty).isEqualTo("prodValue");
+    }
+}