Add missing debug(Writer) alternative

See gh-33059

Author: snicoll

spring-test/src/main/java/org/springframework/test/web/servlet/assertj/MvcTestResultAssert.java

@@ -21,6 +21,7 @@
 import java.io.PrintWriter;
 import java.io.StringReader;
 import java.io.StringWriter;
+import java.io.Writer;
 
 import jakarta.servlet.http.Cookie;
 import org.assertj.core.api.AbstractStringAssert;
@@ -158,6 +159,16 @@ public MvcTestResultAssert debug(OutputStream stream) {
 		return apply(MockMvcResultHandlers.print(stream));
 	}
 
+	/**
+	 * Print {@link MvcResult} details to the supplied {@link Writer}.
+	 * <p>You must call it <b>before</b> calling the assertion otherwise it is ignored
+	 * as the failing assertion breaks the chained call by throwing an
+	 * AssertionError.
+	 */
+	public MvcTestResultAssert debug(Writer writer) {
+		return apply(MockMvcResultHandlers.print(writer));
+	}
+
 	/**
 	 * Verify that the request has failed.
 	 */

spring-test/src/test/java/org/springframework/test/web/servlet/assertj/MockMvcTesterIntegrationTests.java

@@ -18,6 +18,7 @@
 
 import java.io.ByteArrayOutputStream;
 import java.io.PrintStream;
+import java.io.StringWriter;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.HashMap;
@@ -357,6 +358,15 @@ void debugCanPrintToCustomOutputStream() {
 			assertThat(capturedOut()).isEmpty();
 		}
 
+		@Test
+		void debugCanPrintToCustomWriter() {
+			StringWriter out = new StringWriter();
+			assertThat(mvc.get().uri("/greet")).debug(out).hasStatusOk();
+			assertThat(out.toString())
+					.contains("MockHttpServletRequest:", "MockHttpServletResponse:");
+			assertThat(capturedOut()).isEmpty();
+		}
+
 		private String capturedOut() {
 			return this.capturedOut.toString(StandardCharsets.UTF_8);
 		}