Fix failing tests

See gh-26746

spring-core/src/testFixtures/java/org/springframework/core/testfixture/io/buffer/AbstractDataBufferAllocatingTests.java

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 import java.time.Instant;
@@ -89,8 +90,12 @@ public abstract class AbstractDataBufferAllocatingTests {
 	}
 
 	protected Consumer<DataBuffer> stringConsumer(String expected) {
+		return stringConsumer(expected, UTF_8);
+	}
+
+	protected Consumer<DataBuffer> stringConsumer(String expected, Charset charset) {
 		return dataBuffer -> {
-			String value = dataBuffer.toString(UTF_8);
+			String value = dataBuffer.toString(charset);
 			DataBufferUtils.release(dataBuffer);
 			assertThat(value).isEqualTo(expected);
 		};

spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageWriterTests.java

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -150,8 +150,12 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 		testWrite(source, outputMessage, Pojo.class);
 
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(stringConsumer("data:{\"foo\":\"foofoo\",\"bar\":\"barbar\"}\n\n"))
-				.consumeNextWith(stringConsumer("data:{\"foo\":\"foofoofoo\",\"bar\":\"barbarbar\"}\n\n"))
+				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("{\"foo\":\"foofoo\",\"bar\":\"barbar\"}"))
+				.consumeNextWith(stringConsumer("\n\n"))
+				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("{\"foo\":\"foofoofoo\",\"bar\":\"barbarbar\"}"))
+				.consumeNextWith(stringConsumer("\n\n"))
 				.expectComplete()
 				.verify();
 	}
@@ -168,12 +172,16 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 		testWrite(source, outputMessage, Pojo.class);
 
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(stringConsumer("data:{\n" +
+				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("{\n" +
 						"data:  \"foo\" : \"foofoo\",\n" +
-						"data:  \"bar\" : \"barbar\"\n" + "data:}\n\n"))
-				.consumeNextWith(stringConsumer("data:{\n" +
+						"data:  \"bar\" : \"barbar\"\n" + "data:}"))
+				.consumeNextWith(stringConsumer("\n\n"))
+				.consumeNextWith(stringConsumer("data:"))
+				.consumeNextWith(stringConsumer("{\n" +
 						"data:  \"foo\" : \"foofoofoo\",\n" +
-						"data:  \"bar\" : \"barbarbar\"\n" + "data:}\n\n"))
+						"data:  \"bar\" : \"barbarbar\"\n" + "data:}"))
+				.consumeNextWith(stringConsumer("\n\n"))
 				.expectComplete()
 				.verify();
 	}
@@ -190,11 +198,9 @@ class ServerSentEventHttpMessageWriterTests extends AbstractDataBufferAllocating
 
 		assertThat(outputMessage.getHeaders().getContentType()).isEqualTo(mediaType);
 		StepVerifier.create(outputMessage.getBody())
-				.consumeNextWith(dataBuffer -> {
-					String value = dataBuffer.toString(charset);
-					DataBufferUtils.release(dataBuffer);
-					assertThat(value).isEqualTo("data:{\"foo\":\"foo\uD834\uDD1E\",\"bar\":\"bar\uD834\uDD1E\"}\n\n");
-				})
+				.consumeNextWith(stringConsumer("data:", charset))
+				.consumeNextWith(stringConsumer("{\"foo\":\"foo\uD834\uDD1E\",\"bar\":\"bar\uD834\uDD1E\"}", charset))
+				.consumeNextWith(stringConsumer("\n\n", charset))
 				.expectComplete()
 				.verify();
 	}