Update 35.4.3. OutputCapture.md

IV. Spring Boot features/35.4.3. OutputCapture.md

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+### 35.4.3. OutputCapture
+
+OutputCapture是一个JUnit Rule，用于捕获System.out和System.err输出。只需简单的将捕获声明为一个@Rule，并使用toString()断言：
+```java
+import org.junit.Rule;
+import org.junit.Test;
+import org.springframework.boot.test.OutputCapture;
+import static org.hamcrest.Matchers.*;
+import static org.junit.Assert.*;
+
+public class MyTest {
+@Rule
+public OutputCapture capture = new OutputCapture();
+@Test
+public void testName() throws Exception {
+System.out.println("Hello World!");
+assertThat(capture.toString(), containsString("World"));
+}
+}
+```