Add a test for `unused_allocation` lint

(how come we didn't have one already??)

2 files changed, 27 insertions, 0 deletions

diff --git a/tests/ui/lint/unused/unused-allocation.rs b/tests/ui/lint/unused/unused-allocation.rs
new file mode 100644
index 00000000000..df51dd194d5
--- /dev/null
+++ b/tests/ui/lint/unused/unused-allocation.rs
@@ -0,0 +1,7 @@
+#![feature(box_syntax)]
+#![deny(unused_allocation)]
+
+fn main() {
+    _ = (box [1]).len(); //~ error: unnecessary allocation, use `&` instead
+    _ = Box::new([1]).len(); //~ error: unnecessary allocation, use `&` instead
+}
diff --git a/tests/ui/lint/unused/unused-allocation.stderr b/tests/ui/lint/unused/unused-allocation.stderr
new file mode 100644
index 00000000000..91bd1da35a3
--- /dev/null
+++ b/tests/ui/lint/unused/unused-allocation.stderr
@@ -0,0 +1,20 @@
+error: unnecessary allocation, use `&` instead
+  --> $DIR/unused-allocation.rs:5:9
+   |
+LL |     _ = (box [1]).len();
+   |         ^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-allocation.rs:2:9
+   |
+LL | #![deny(unused_allocation)]
+   |         ^^^^^^^^^^^^^^^^^
+
+error: unnecessary allocation, use `&` instead
+  --> $DIR/unused-allocation.rs:6:9
+   |
+LL |     _ = Box::new([1]).len();
+   |         ^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+