Inconsistent and misleading? behavior for FluentArgs::set (#271)

* fix FluentArgs::set

* update tests for replacing existing arguments

Author: MathieuTricoire

fluent-bundle/src/args.rs

@@ -74,11 +74,10 @@ impl<'args> FluentArgs<'args> {
         V: Into<FluentValue<'args>>,
     {
         let key = key.into();
-        let idx = match self.0.binary_search_by_key(&&key, |(k, _)| k) {
-            Ok(idx) => idx,
-            Err(idx) => idx,
+        match self.0.binary_search_by_key(&&key, |(k, _)| k) {
+            Ok(idx) => self.0[idx] = (key, value.into()),
+            Err(idx) => self.0.insert(idx, (key, value.into())),
         };
-        self.0.insert(idx, (key, value.into()));
     }
 
     pub fn iter(&self) -> impl Iterator<Item = (&str, &FluentValue)> {
@@ -118,3 +117,31 @@ impl<'args> IntoIterator for FluentArgs<'args> {
         self.0.into_iter()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn replace_existing_arguments() {
+        let mut args = FluentArgs::new();
+
+        args.set("name", "John");
+        args.set("emailCount", 5);
+        assert_eq!(args.0.len(), 2);
+        assert_eq!(
+            args.get("name"),
+            Some(&FluentValue::String(Cow::Borrowed("John")))
+        );
+        assert_eq!(args.get("emailCount"), Some(&FluentValue::try_number(5)));
+
+        args.set("name", "Jane");
+        args.set("emailCount", 7);
+        assert_eq!(args.0.len(), 2);
+        assert_eq!(
+            args.get("name"),
+            Some(&FluentValue::String(Cow::Borrowed("Jane")))
+        );
+        assert_eq!(args.get("emailCount"), Some(&FluentValue::try_number(7)));
+    }
+}