strv: fix join to take &self and add test

Author: pbor

glib/src/collections/strv.rs

@@ -856,7 +856,7 @@ impl StrV {
     /// Joins the strings into a longer string, with an optional separator
     #[inline]
     #[doc(alias = "g_strjoinv")]
-    pub fn join(self, separator: Option<impl IntoGStr>) -> GString {
+    pub fn join(&self, separator: Option<impl IntoGStr>) -> GString {
         separator.run_with_gstr(|separator| unsafe {
             from_glib_full(ffi::g_strjoinv(
                 separator.to_glib_none().0,
@@ -1488,6 +1488,19 @@ mod test {
         });
     }
 
+    #[test]
+    fn test_join() {
+        let items = [
+            crate::gstr!("str1"),
+            crate::gstr!("str2"),
+            crate::gstr!("str3"),
+        ];
+
+        let strv = StrV::from(&items[..]);
+        assert_eq!(strv.join(None::<&str>), "str1str2str3");
+        assert_eq!(strv.join(Some(",")), "str1,str2,str3");
+    }
+
     #[test]
     fn test_contains() {
         let items = [