link to chap 27 in 4

Author: hjwp

chapter_04_philosophy_and_refactoring.asciidoc

@@ -742,6 +742,10 @@ TIP: Unit tests give you faster and more specific feedback than FTs.
   Bear this in mind when deciding what to test where.
 
 
+We'll visit the tradeoffs between different types of tests
+at several points in the book, and particularly in <<chapter_27_hot_lava>>.
+
+
 === On Refactoring
 
 ((("unit tests", "refactoring in")))