2 files changed, 11 insertions, 0 deletions
diff --git a/src/libcoretest/fmt/mod.rs b/src/libcoretest/fmt/mod.rs
index ed33596e1c2..5d204c7d523 100644
--- a/src/libcoretest/fmt/mod.rs
+++ b/src/libcoretest/fmt/mod.rs
@@ -28,3 +28,13 @@ fn test_pointer_formats_data_pointer() {
     assert_eq!(format!("{:p}", s), format!("{:p}", s.as_ptr()));
     assert_eq!(format!("{:p}", b), format!("{:p}", b.as_ptr()));
 }
+
+#[test]
+fn test_estimated_capacity() {
+    assert_eq!(format_args!("").estimated_capacity(), 0);
+    assert_eq!(format_args!("{}", "").estimated_capacity(), 0);
+    assert_eq!(format_args!("Hello").estimated_capacity(), 5);
+    assert_eq!(format_args!("Hello, {}!", "").estimated_capacity(), 16);
+    assert_eq!(format_args!("{}, hello!", "World").estimated_capacity(), 0);
+    assert_eq!(format_args!("{}. 16-bytes piece", "World").estimated_capacity(), 32);
+}
diff --git a/src/libcoretest/lib.rs b/src/libcoretest/lib.rs
index 87f3afd6889..e06b757691e 100644
--- a/src/libcoretest/lib.rs
+++ b/src/libcoretest/lib.rs
@@ -34,6 +34,7 @@
 #![feature(ordering_chaining)]
 #![feature(ptr_unaligned)]
 #![feature(move_cell)]
+#![feature(fmt_internals)]
 
 extern crate core;
 extern crate test;