Fix clippy install. Add more illustrative remap tests

.travis.yml

@@ -30,8 +30,7 @@ script:
   - if [ "$LANGUAGE" == "Rust" ]; then cargo build --verbose; fi
   - if [ "$LANGUAGE" == "Rust" ]; then cargo test  --verbose; fi
   - if [ "$LANGUAGE" == "Rust" ] && [ "$CLIPPY" ]; then
-      cargo install clippy cargo-update;
-      cargo install-update -a;
+      cargo install -f clippy;
       cargo clippy;
     fi
 

tests/dialect/remap.rs

@@ -32,3 +32,26 @@ fn hard() {
 
     assert_eq!(mapping.decode(0x41), 'Ź');
 }
+
+#[test]
+fn double() {
+    assert_eq!(CP437_WINGDINGS.encode('Ź'), None);
+    assert_eq!(CP437_WINGDINGS.encode('A'), Some(0x41));
+    assert_eq!(CP437_WINGDINGS.encode('√'), Some(0xFB));
+    assert_eq!(CP437_WINGDINGS.encode('✓'), Some(0xFB));
+
+    assert_eq!(CP437_WINGDINGS.decode(0x41), 'A');
+    assert_eq!(CP437_WINGDINGS.decode(0xFB), '√');
+
+    let mut mapping = CP437_WINGDINGS.clone();
+    mapping.remap(0x41, 'Ź');
+    mapping.remap(0xFB, '✓');
+
+    assert_eq!(mapping.encode('Ź'), Some(0x41));
+    assert_eq!(mapping.encode('A'), Some(0x41)); // NB: still holds
+    assert_eq!(mapping.encode('√'), Some(0xFB));
+    assert_eq!(mapping.encode('✓'), Some(0xFB));
+
+    assert_eq!(mapping.decode(0x41), 'Ź');
+    assert_eq!(mapping.decode(0xFB), '✓');
+}