diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/rustfmt.toml b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/rustfmt.toml
new file mode 100644
index 0000000000..e1b84c3342
--- /dev/null
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/rustfmt.toml
@@ -0,0 +1,2 @@
+max_width = 120
+match_block_trailing_comma = true
diff --git a/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/rustfmt.toml b/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/rustfmt.toml
new file mode 100644
index 0000000000..9b630818e2
--- /dev/null
+++ b/test/rubygems/test_gem_ext_cargo_builder/rust_ruby_example/rustfmt.toml
@@ -0,0 +1,2 @@
+max_width = 300
+match_block_trailing_comma = true