1 files changed, 144 insertions, 0 deletions
diff --git a/library/alloc/tests/cow_str.rs b/library/alloc/tests/cow_str.rs
new file mode 100644
index 000000000..62a5c245a
--- /dev/null
+++ b/library/alloc/tests/cow_str.rs
@@ -0,0 +1,144 @@
+use std::borrow::Cow;
+
+// check that Cow<'a, str> implements addition
+#[test]
+fn check_cow_add_cow() {
+    let borrowed1 = Cow::Borrowed("Hello, ");
+    let borrowed2 = Cow::Borrowed("World!");
+    let borrow_empty = Cow::Borrowed("");
+
+    let owned1: Cow<'_, str> = Cow::Owned(String::from("Hi, "));
+    let owned2: Cow<'_, str> = Cow::Owned(String::from("Rustaceans!"));
+    let owned_empty: Cow<'_, str> = Cow::Owned(String::new());
+
+    assert_eq!("Hello, World!", borrowed1.clone() + borrowed2.clone());
+    assert_eq!("Hello, Rustaceans!", borrowed1.clone() + owned2.clone());
+
+    assert_eq!("Hi, World!", owned1.clone() + borrowed2.clone());
+    assert_eq!("Hi, Rustaceans!", owned1.clone() + owned2.clone());
+
+    if let Cow::Owned(_) = borrowed1.clone() + borrow_empty.clone() {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    if let Cow::Owned(_) = borrow_empty.clone() + borrowed1.clone() {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    if let Cow::Owned(_) = borrowed1.clone() + owned_empty.clone() {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    if let Cow::Owned(_) = owned_empty.clone() + borrowed1.clone() {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+}
+
+#[test]
+fn check_cow_add_str() {
+    let borrowed = Cow::Borrowed("Hello, ");
+    let borrow_empty = Cow::Borrowed("");
+
+    let owned: Cow<'_, str> = Cow::Owned(String::from("Hi, "));
+    let owned_empty: Cow<'_, str> = Cow::Owned(String::new());
+
+    assert_eq!("Hello, World!", borrowed.clone() + "World!");
+
+    assert_eq!("Hi, World!", owned.clone() + "World!");
+
+    if let Cow::Owned(_) = borrowed.clone() + "" {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    if let Cow::Owned(_) = borrow_empty.clone() + "Hello, " {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    if let Cow::Owned(_) = owned_empty.clone() + "Hello, " {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+}
+
+#[test]
+fn check_cow_add_assign_cow() {
+    let mut borrowed1 = Cow::Borrowed("Hello, ");
+    let borrowed2 = Cow::Borrowed("World!");
+    let borrow_empty = Cow::Borrowed("");
+
+    let mut owned1: Cow<'_, str> = Cow::Owned(String::from("Hi, "));
+    let owned2: Cow<'_, str> = Cow::Owned(String::from("Rustaceans!"));
+    let owned_empty: Cow<'_, str> = Cow::Owned(String::new());
+
+    let mut s = borrowed1.clone();
+    s += borrow_empty.clone();
+    assert_eq!("Hello, ", s);
+    if let Cow::Owned(_) = s {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    let mut s = borrow_empty.clone();
+    s += borrowed1.clone();
+    assert_eq!("Hello, ", s);
+    if let Cow::Owned(_) = s {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    let mut s = borrowed1.clone();
+    s += owned_empty.clone();
+    assert_eq!("Hello, ", s);
+    if let Cow::Owned(_) = s {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    let mut s = owned_empty.clone();
+    s += borrowed1.clone();
+    assert_eq!("Hello, ", s);
+    if let Cow::Owned(_) = s {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+
+    owned1 += borrowed2;
+    borrowed1 += owned2;
+
+    assert_eq!("Hi, World!", owned1);
+    assert_eq!("Hello, Rustaceans!", borrowed1);
+}
+
+#[test]
+fn check_cow_add_assign_str() {
+    let mut borrowed = Cow::Borrowed("Hello, ");
+    let borrow_empty = Cow::Borrowed("");
+
+    let mut owned: Cow<'_, str> = Cow::Owned(String::from("Hi, "));
+    let owned_empty: Cow<'_, str> = Cow::Owned(String::new());
+
+    let mut s = borrowed.clone();
+    s += "";
+    assert_eq!("Hello, ", s);
+    if let Cow::Owned(_) = s {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    let mut s = borrow_empty.clone();
+    s += "World!";
+    assert_eq!("World!", s);
+    if let Cow::Owned(_) = s {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+    let mut s = owned_empty.clone();
+    s += "World!";
+    assert_eq!("World!", s);
+    if let Cow::Owned(_) = s {
+        panic!("Adding empty strings to a borrow should note allocate");
+    }
+
+    owned += "World!";
+    borrowed += "World!";
+
+    assert_eq!("Hi, World!", owned);
+    assert_eq!("Hello, World!", borrowed);
+}
+
+#[test]
+fn check_cow_clone_from() {
+    let mut c1: Cow<'_, str> = Cow::Owned(String::with_capacity(25));
+    let s: String = "hi".to_string();
+    assert!(s.capacity() < 25);
+    let c2: Cow<'_, str> = Cow::Owned(s);
+    c1.clone_from(&c2);
+    assert!(c1.into_owned().capacity() >= 25);
+    let mut c3: Cow<'_, str> = Cow::Borrowed("bye");
+    c3.clone_from(&c2);
+    assert_eq!(c2, c3);
+}