Add note about test generation depth

diff --git a/src/libraries/System.Text.Json/tests/Serialization/DictionaryTests.cs b/src/libraries/System.Text.Json/tests/Serialization/DictionaryTests.cs
index cbd3b6e..dfdeb5c 100644 (file)
--- a/src/libraries/System.Text.Json/tests/Serialization/DictionaryTests.cs
+++ b/src/libraries/System.Text.Json/tests/Serialization/DictionaryTests.cs
@@ -997,6 +997,9 @@ namespace System.Text.Json.Serialization.Tests
             };
             baseDictionaryTypes.AddRange(nonGenericDictTypes);
 
+            // This method has exponential behavior which this depth value significantly impacts.
+            // Don't change this value without checking how many test cases are generated and
+            // how long the tests run for.
             int maxTestDepth = 4;
 
             HashSet<(Type, string)> tests = new HashSet<(Type, string)>();