Build in operators between string and char.

tests/decrement.rs

@@ -6,10 +6,10 @@ fn test_decrement() -> Result<(), Box<EvalAltResult>> {
 
     assert_eq!(engine.eval::<INT>("let x = 10; x -= 7; x")?, 3);
 
-    assert!(matches!(
-        *engine.eval::<String>(r#"let s = "test"; s -= "ing"; s"#).expect_err("expects error"),
-        EvalAltResult::ErrorFunctionNotFound(err, _) if err == "- (&str | ImmutableString | String, &str | ImmutableString | String)"
-    ));
+    assert_eq!(
+        engine.eval::<String>(r#"let s = "test"; s -= 's'; s"#)?,
+        "tet"
+    );
 
     Ok(())
 }

tests/increment.rs

@@ -7,7 +7,7 @@ fn test_increment() -> Result<(), Box<EvalAltResult>> {
     assert_eq!(engine.eval::<INT>("let x = 1; x += 2; x")?, 3);
 
     assert_eq!(
-        engine.eval::<String>("let s = \"test\"; s += \"ing\"; s")?,
+        engine.eval::<String>(r#"let s = "test"; s += "ing"; s"#)?,
         "testing"
     );
 

tests/ops.rs

@@ -34,7 +34,19 @@ fn test_ops_numbers() -> Result<(), Box<EvalAltResult>> {
 }
 
 #[test]
-fn test_op_precedence() -> Result<(), Box<EvalAltResult>> {
+fn test_ops_strings() -> Result<(), Box<EvalAltResult>> {
+    let engine = Engine::new();
+
+    assert!(engine.eval::<bool>(r#""hello" > 'c'"#)?);
+    assert!(engine.eval::<bool>(r#""" < 'c'"#)?);
+    assert!(engine.eval::<bool>(r#"'x' > "hello""#)?);
+    assert!(engine.eval::<bool>(r#""hello" > "foo""#)?);
+
+    Ok(())
+}
+
+#[test]
+fn test_ops_precedence() -> Result<(), Box<EvalAltResult>> {
     let engine = Engine::new();
 
     assert_eq!(

tests/string.rs

@@ -132,6 +132,19 @@ fn test_string_substring() -> Result<(), Box<EvalAltResult>> {
         "❤❤ hello! ❤❤❤"
     );
 
+    assert_eq!(
+        engine.eval::<String>(
+            r#"let x = "\u2764\u2764\u2764 hello! \u2764\u2764\u2764"; x -= 'l'; x"#
+        )?,
+        "❤❤❤ heo! ❤❤❤"
+    );
+
+    assert_eq!(
+        engine.eval::<String>(
+            r#"let x = "\u2764\u2764\u2764 hello! \u2764\u2764\u2764"; x -= "\u2764\u2764"; x"#
+        )?,
+        "❤ hello! ❤"
+    );
     assert_eq!(
         engine.eval::<INT>(
             r#"let x = "\u2764\u2764\u2764 hello! \u2764\u2764\u2764"; x.index_of('\u2764')"#