keyfork-mnemonic-generate: add failing test to track birthday paradox

keyfork-mnemonic-generate/src/main.rs

@@ -94,7 +94,7 @@ fn ensure_offline() {
 // TODO: Can a Mnemonic be formatted using a wordlist, without allocating or without storing the
 // entire word list?
 struct Mnemonic {
-    words: Vec<usize>,
+    pub words: Vec<usize>,
     wordlist: Vec<String>,
 }
 
@@ -232,4 +232,20 @@ mod tests {
         }
         Ok(())
     }
+
+    #[test]
+    fn count_to_get_duplicate_words() {
+        let mut count = 0.;
+        let mut random_handle = File::open("/dev/urandom").unwrap();
+        let entropy = &mut [0u8; 256 / 8];
+        for _ in 0..100_000 {
+            random_handle.read_exact(&mut entropy[..]).unwrap();
+            let mut mnemonic = Mnemonic::from_entropy(&entropy[..256 / 8]).unwrap();
+            mnemonic.words.dedup();
+            if mnemonic.words.len() != 24 {
+                count += 1.;
+            }
+        }
+        panic!("counts: {count} {}", count / 100_000.)
+    }
 }