Add boundary tests for JsonValueWriter max nesting depth

Verify behavior at the maxNestingDepth boundary.

Signed-off-by: Joowon-Seo <tjwndnjs1998@gmail.com>

See gh-49662

Author: Joowon-Seo

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/json/JsonValueWriterTests.java

@@ -296,6 +296,38 @@ void illegalStateExceptionShouldBeThrownWhenIterableExceededNestingDepth() {
 					"JSON nesting depth (129) exceeds maximum depth of 128 (current path: [0][0][0][0][0][0][0][0][0][0][0][0]");
 	}
 
+	@Test
+	void shouldAllowStartingObjectWhenCurrentDepthIsMaxDepth() {
+		StringBuilder out = new StringBuilder();
+		JsonValueWriter writer = new JsonValueWriter(out, 2);
+
+		writer.start(Series.OBJECT);
+		writer.start(Series.OBJECT);
+		writer.start(Series.OBJECT);
+
+		writer.end(Series.OBJECT);
+		writer.end(Series.OBJECT);
+		writer.end(Series.OBJECT);
+
+		assertThat(out).hasToString("{{{}}}");
+	}
+
+	@Test
+	void shouldAllowStartingArrayWhenCurrentDepthIsMaxDepth() {
+		StringBuilder out = new StringBuilder();
+		JsonValueWriter writer = new JsonValueWriter(out, 2);
+
+		writer.start(Series.ARRAY);
+		writer.start(Series.ARRAY);
+		writer.start(Series.ARRAY);
+
+		writer.end(Series.ARRAY);
+		writer.end(Series.ARRAY);
+		writer.end(Series.ARRAY);
+
+		assertThat(out).hasToString("[[[]]]");
+	}
+
 	private <V> String write(V value) {
 		return doWrite((valueWriter) -> valueWriter.write(value));
 	}