BAEL-3741: Add usage examples of @TestPropertySource (#8493)

spring-boot-properties/src/test/java/com/baeldung/properties/testproperty/FilePropertyInjectionUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.properties.testproperty;
+
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(SpringRunner.class)
+@TestPropertySource("/foo.properties")
+public class FilePropertyInjectionUnitTest {
+
+    @Value("${foo}")
+    private String foo;
+
+    @Test
+    public void whenFilePropertyProvided_thenProperlyInjected() {
+        assertThat(foo).isEqualTo("bar");
+    }
+}

spring-boot-properties/src/test/java/com/baeldung/properties/testproperty/PropertyInjectionUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.properties.testproperty;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(SpringRunner.class)
+@TestPropertySource(properties = {"foo=bar"})
+public class PropertyInjectionUnitTest {
+
+    @Value("${foo}")
+    private String foo;
+
+    @Test
+    public void whenPropertyProvided_thenProperlyInjected() {
+        assertThat(foo).isEqualTo("bar");
+    }
+}

spring-boot-properties/src/test/java/com/baeldung/properties/testproperty/SpringBootPropertyInjectionIntegrationTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.properties.testproperty;
+
+import com.baeldung.properties.reloading.SpringBootPropertiesTestApplication;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest(properties = {"foo=bar"}, classes = SpringBootPropertiesTestApplication.class)
+public class SpringBootPropertyInjectionIntegrationTest {
+
+    @Value("${foo}")
+    private String foo;
+
+    @Test
+    public void whenSpringBootPropertyProvided_thenProperlyInjected() {
+        assertThat(foo).isEqualTo("bar");
+    }
+}

spring-boot-properties/src/test/resources/foo.properties

@@ -0,0 +1 @@
+foo=bar