diff --git a/tests/ui-cargo/mixed_attributes_style/fail/Cargo.stderr b/tests/ui-cargo/mixed_attributes_style/fail/Cargo.stderr
new file mode 100644
index 000000000000..4fafd29bb502
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/fail/Cargo.stderr
@@ -0,0 +1,12 @@
+error: item has both inner and outer attributes
+ --> src/submodule.rs:1:1
+  |
+1 | / #[allow(unused)]
+2 | | mod foo {
+3 | |     #![allow(dead_code)]
+  | |________________________^
+  |
+  = note: `-D clippy::mixed-attributes-style` implied by `-D warnings`
+  = help: to override `-D warnings` add `#[allow(clippy::mixed_attributes_style)]`
+
+error: could not compile `mixed_attributes_style` (bin "mixed_attributes_style") due to 1 previous error
diff --git a/tests/ui-cargo/mixed_attributes_style/fail/Cargo.toml b/tests/ui-cargo/mixed_attributes_style/fail/Cargo.toml
new file mode 100644
index 000000000000..13c9996c9bde
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/fail/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "mixed_attributes_style"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
diff --git a/tests/ui-cargo/mixed_attributes_style/fail/src/main.rs b/tests/ui-cargo/mixed_attributes_style/fail/src/main.rs
new file mode 100644
index 000000000000..f6a2037ad0be
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/fail/src/main.rs
@@ -0,0 +1,2 @@
+mod submodule;
+fn main() {}
diff --git a/tests/ui-cargo/mixed_attributes_style/fail/src/submodule.rs b/tests/ui-cargo/mixed_attributes_style/fail/src/submodule.rs
new file mode 100644
index 000000000000..acfc561835f8
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/fail/src/submodule.rs
@@ -0,0 +1,4 @@
+#[allow(unused)]
+mod foo {
+    #![allow(dead_code)]
+}
diff --git a/tests/ui-cargo/mixed_attributes_style/pass/Cargo.stderr b/tests/ui-cargo/mixed_attributes_style/pass/Cargo.stderr
new file mode 100644
index 000000000000..4fafd29bb502
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/pass/Cargo.stderr
@@ -0,0 +1,12 @@
+error: item has both inner and outer attributes
+ --> src/submodule.rs:1:1
+  |
+1 | / #[allow(unused)]
+2 | | mod foo {
+3 | |     #![allow(dead_code)]
+  | |________________________^
+  |
+  = note: `-D clippy::mixed-attributes-style` implied by `-D warnings`
+  = help: to override `-D warnings` add `#[allow(clippy::mixed_attributes_style)]`
+
+error: could not compile `mixed_attributes_style` (bin "mixed_attributes_style") due to 1 previous error
diff --git a/tests/ui-cargo/mixed_attributes_style/pass/Cargo.toml b/tests/ui-cargo/mixed_attributes_style/pass/Cargo.toml
new file mode 100644
index 000000000000..13c9996c9bde
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/pass/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "mixed_attributes_style"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
diff --git a/tests/ui-cargo/mixed_attributes_style/pass/src/main.rs b/tests/ui-cargo/mixed_attributes_style/pass/src/main.rs
new file mode 100644
index 000000000000..8ea851e0910a
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/pass/src/main.rs
@@ -0,0 +1,4 @@
+// Issue #12436
+#![allow(clippy::mixed_attributes_style)]
+mod submodule;
+fn main() {}
diff --git a/tests/ui-cargo/mixed_attributes_style/pass/src/submodule.rs b/tests/ui-cargo/mixed_attributes_style/pass/src/submodule.rs
new file mode 100644
index 000000000000..acfc561835f8
--- /dev/null
+++ b/tests/ui-cargo/mixed_attributes_style/pass/src/submodule.rs
@@ -0,0 +1,4 @@
+#[allow(unused)]
+mod foo {
+    #![allow(dead_code)]
+}