Add function tests

This CL adds tests for the function node.

Bug: tint:11
Change-Id: I10b1fb73ae93bf90162948ab42e2a74d4aca7987
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/16501
Reviewed-by: Sarah Mashayekhi <sarahmashay@google.com>
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3e0cc62..05c61bb 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -209,6 +209,7 @@
   ast/else_statement_test.cc
   ast/entry_point_test.cc
   ast/fallthrough_statement_test.cc
+  ast/function_test.cc
   ast/import_test.cc
   ast/int_literal_test.cc
   ast/location_decoration_test.cc