another codewars solution

codewars_kata_training/examples/main.rs

@@ -15,6 +15,39 @@ mod array_diff_tests {
     }
 }
 
+
+#[cfg(test)]
+mod duplicate_counter_tests {
+    use std::collections::HashMap;
+
+    fn count_duplicates(text: &str) -> u32 {
+        let mut char_count = HashMap::new();
+
+        for c in text.to_lowercase().chars() {
+            if c.is_alphanumeric() {
+                *char_count.entry(c).or_insert(0) += 1;
+            }
+        }
+
+        char_count.values().filter(|&count| *count > 1).count() as u32
+    }
+
+    #[test]
+    fn test_abcde() {
+        assert_eq!(count_duplicates("abcde"), 0);
+    }
+
+    #[test]
+    fn test_abcdea() {
+        assert_eq!(count_duplicates("abcdea"), 1);
+    }
+
+    #[test]
+    fn test_indivisibility() {
+        assert_eq!(count_duplicates("indivisibility"), 1);
+    }
+}
+
 #[cfg(test)]
 mod break_camelcase_tests {
     fn solution(s: &str) -> String {