add tests for slow path joining

old tests cover the new fast paths already
this adds tests for joining into Strings with long separators (>4 byte) and
joining into Vec<T>, T: !Copy

Author: Emerentius

src/liballoc/tests/slice.rs

@@ -609,6 +609,20 @@ fn test_join() {
     assert_eq!(v.join(&0), [1, 0, 2, 0, 3]);
 }
 
+#[test]
+fn test_join_nocopy() {
+    let v: [Vec<String>; 0] = [];
+    let comma = String::new(",");
+    assert_eq!(v.join(&",".into()), []);
+    assert_eq!(["a".into(), "ab".into()].join(comma), "a,ab");
+    assert_eq!(["a".into(), "ab".into(), "abc".into()].join(comma), "a,ab,abc");
+
+    let v: [&[_]; 2] = [&["a".into()], &["a".into(), "b".into()]];
+    assert_eq!(v.join(comma), "a,ab");
+    let v: [&[_]; 2] = [&["a".into()], &["b".into()], ["c".into()]];
+    assert_eq!(v.join(comma), "a,b,c");
+}
+
 #[test]
 fn test_insert() {
     let mut a = vec![1, 2, 4];

src/liballoc/tests/str.rs

@@ -162,6 +162,19 @@ fn test_join_for_different_lengths() {
     test_join!("-a-bc", ["", "a", "bc"], "-");
 }
 
+// join has fast paths for small separators up to 4 bytes
+// this tests the slow paths.
+#[test]
+fn test_join_for_different_lengths_with_long_separator() {
+    assert_eq!("～～～～～".len(), 15);
+
+    let empty: &[&str] = &[];
+    test_join!("", empty, "～～～～～");
+    test_join!("a", ["a"], "～～～～～");
+    test_join!("a～～～～～b", ["a", "b"], "～～～～～");
+    test_join!("～～～～～a～～～～～bc", ["", "a", "bc"], "～～～～～");
+}
+
 #[test]
 fn test_unsafe_slice() {
     assert_eq!("ab", unsafe {"abc".slice_unchecked(0, 2)});