diff --git a/tests/ui/string_add.rs b/tests/ui/string_add.rs
new file mode 100644
index 00000000000..c9dd13eea8a
--- /dev/null
+++ b/tests/ui/string_add.rs
@@ -0,0 +1,19 @@
+#[warn(clippy::string_add)]
+#[allow(clippy::string_add_assign, unused)]
+fn main() {
+    // ignores assignment distinction
+    let mut x = "".to_owned();
+
+    for _ in 1..3 {
+        x = x + ".";
+    }
+
+    let y = "".to_owned();
+    let z = y + "...";
+
+    assert_eq!(&x, &z);
+
+    let mut x = 1;
+    x = x + 1;
+    assert_eq!(2, x);
+}
diff --git a/tests/ui/string_add.stderr b/tests/ui/string_add.stderr
new file mode 100644
index 00000000000..8345c50f971
--- /dev/null
+++ b/tests/ui/string_add.stderr
@@ -0,0 +1,30 @@
+error: manual implementation of an assign operation
+  --> $DIR/string_add.rs:8:9
+   |
+LL |         x = x + ".";
+   |         ^^^^^^^^^^^ help: replace it with: `x += "."`
+   |
+   = note: `-D clippy::assign-op-pattern` implied by `-D warnings`
+
+error: you added something to a string. Consider using `String::push_str()` instead
+  --> $DIR/string_add.rs:8:13
+   |
+LL |         x = x + ".";
+   |             ^^^^^^^
+   |
+   = note: `-D clippy::string-add` implied by `-D warnings`
+
+error: you added something to a string. Consider using `String::push_str()` instead
+  --> $DIR/string_add.rs:12:13
+   |
+LL |     let z = y + "...";
+   |             ^^^^^^^^^
+
+error: manual implementation of an assign operation
+  --> $DIR/string_add.rs:17:5
+   |
+LL |     x = x + 1;
+   |     ^^^^^^^^^ help: replace it with: `x += 1`
+
+error: aborting due to 4 previous errors
+
diff --git a/tests/ui/string_add_assign.fixed b/tests/ui/string_add_assign.fixed
new file mode 100644
index 00000000000..db71bab1e52
--- /dev/null
+++ b/tests/ui/string_add_assign.fixed
@@ -0,0 +1,21 @@
+// run-rustfix
+
+#[allow(clippy::string_add, unused)]
+#[warn(clippy::string_add_assign)]
+fn main() {
+    // ignores assignment distinction
+    let mut x = "".to_owned();
+
+    for _ in 1..3 {
+        x += ".";
+    }
+
+    let y = "".to_owned();
+    let z = y + "...";
+
+    assert_eq!(&x, &z);
+
+    let mut x = 1;
+    x += 1;
+    assert_eq!(2, x);
+}
diff --git a/tests/ui/string_add_assign.rs b/tests/ui/string_add_assign.rs
new file mode 100644
index 00000000000..644991945cb
--- /dev/null
+++ b/tests/ui/string_add_assign.rs
@@ -0,0 +1,21 @@
+// run-rustfix
+
+#[allow(clippy::string_add, unused)]
+#[warn(clippy::string_add_assign)]
+fn main() {
+    // ignores assignment distinction
+    let mut x = "".to_owned();
+
+    for _ in 1..3 {
+        x = x + ".";
+    }
+
+    let y = "".to_owned();
+    let z = y + "...";
+
+    assert_eq!(&x, &z);
+
+    let mut x = 1;
+    x = x + 1;
+    assert_eq!(2, x);
+}
diff --git a/tests/ui/string_add_assign.stderr b/tests/ui/string_add_assign.stderr
new file mode 100644
index 00000000000..7676175c1b8
--- /dev/null
+++ b/tests/ui/string_add_assign.stderr
@@ -0,0 +1,24 @@
+error: you assigned the result of adding something to this string. Consider using `String::push_str()` instead
+  --> $DIR/string_add_assign.rs:10:9
+   |
+LL |         x = x + ".";
+   |         ^^^^^^^^^^^
+   |
+   = note: `-D clippy::string-add-assign` implied by `-D warnings`
+
+error: manual implementation of an assign operation
+  --> $DIR/string_add_assign.rs:10:9
+   |
+LL |         x = x + ".";
+   |         ^^^^^^^^^^^ help: replace it with: `x += "."`
+   |
+   = note: `-D clippy::assign-op-pattern` implied by `-D warnings`
+
+error: manual implementation of an assign operation
+  --> $DIR/string_add_assign.rs:19:5
+   |
+LL |     x = x + 1;
+   |     ^^^^^^^^^ help: replace it with: `x += 1`
+
+error: aborting due to 3 previous errors
+
diff --git a/tests/ui/strings.rs b/tests/ui/strings.rs
deleted file mode 100644
index 766e23c744a..00000000000
--- a/tests/ui/strings.rs
+++ /dev/null
@@ -1,55 +0,0 @@
-#[warn(clippy::string_add)]
-#[allow(clippy::string_add_assign)]
-fn add_only() {
-    // ignores assignment distinction
-    let mut x = "".to_owned();
-
-    for _ in 1..3 {
-        x = x + ".";
-    }
-
-    let y = "".to_owned();
-    let z = y + "...";
-
-    assert_eq!(&x, &z);
-}
-
-#[warn(clippy::string_add_assign)]
-fn add_assign_only() {
-    let mut x = "".to_owned();
-
-    for _ in 1..3 {
-        x = x + ".";
-    }
-
-    let y = "".to_owned();
-    let z = y + "...";
-
-    assert_eq!(&x, &z);
-}
-
-#[warn(clippy::string_add, clippy::string_add_assign)]
-fn both() {
-    let mut x = "".to_owned();
-
-    for _ in 1..3 {
-        x = x + ".";
-    }
-
-    let y = "".to_owned();
-    let z = y + "...";
-
-    assert_eq!(&x, &z);
-}
-
-#[allow(clippy::assign_op_pattern)]
-fn main() {
-    add_only();
-    add_assign_only();
-    both();
-
-    // the add is only caught for `String`
-    let mut x = 1;
-    x = x + 1;
-    assert_eq!(2, x);
-}
diff --git a/tests/ui/strings.stderr b/tests/ui/strings.stderr
deleted file mode 100644
index 7f684fe6355..00000000000
--- a/tests/ui/strings.stderr
+++ /dev/null
@@ -1,56 +0,0 @@
-error: manual implementation of an assign operation
-  --> $DIR/strings.rs:8:9
-   |
-LL |         x = x + ".";
-   |         ^^^^^^^^^^^ help: replace it with: `x += "."`
-   |
-   = note: `-D clippy::assign-op-pattern` implied by `-D warnings`
-
-error: you added something to a string. Consider using `String::push_str()` instead
-  --> $DIR/strings.rs:8:13
-   |
-LL |         x = x + ".";
-   |             ^^^^^^^
-   |
-   = note: `-D clippy::string-add` implied by `-D warnings`
-
-error: you added something to a string. Consider using `String::push_str()` instead
-  --> $DIR/strings.rs:12:13
-   |
-LL |     let z = y + "...";
-   |             ^^^^^^^^^
-
-error: you assigned the result of adding something to this string. Consider using `String::push_str()` instead
-  --> $DIR/strings.rs:22:9
-   |
-LL |         x = x + ".";
-   |         ^^^^^^^^^^^
-   |
-   = note: `-D clippy::string-add-assign` implied by `-D warnings`
-
-error: manual implementation of an assign operation
-  --> $DIR/strings.rs:22:9
-   |
-LL |         x = x + ".";
-   |         ^^^^^^^^^^^ help: replace it with: `x += "."`
-
-error: you assigned the result of adding something to this string. Consider using `String::push_str()` instead
-  --> $DIR/strings.rs:36:9
-   |
-LL |         x = x + ".";
-   |         ^^^^^^^^^^^
-
-error: manual implementation of an assign operation
-  --> $DIR/strings.rs:36:9
-   |
-LL |         x = x + ".";
-   |         ^^^^^^^^^^^ help: replace it with: `x += "."`
-
-error: you added something to a string. Consider using `String::push_str()` instead
-  --> $DIR/strings.rs:40:13
-   |
-LL |     let z = y + "...";
-   |             ^^^^^^^^^
-
-error: aborting due to 8 previous errors
-