diff --git a/functions.qmd b/functions.qmd
index 143a560..91cc421 100644
--- a/functions.qmd
+++ b/functions.qmd
@@ -122,7 +122,7 @@ rescale01(c(1, 2, 3, NA, 5))
 
 As you write more and more functions you'll eventually want to convert these informal, interactive tests into formal, automated tests.
 That process is called unit testing.
-Unfortunately, it's beyond the scope of this book, but you can learn about it in <http://r-pkgs.had.co.nz/tests.html>.
+Unfortunately, it's beyond the scope of this book, but you can learn about it in <https://r-pkgs.org/testing-basics.html>.
 
 We can simplify the original example now that we have a function: