Fix contains function expression

datafusion/functions/src/string/contains.rs

@@ -150,10 +150,11 @@ fn contains(args: &[ArrayRef]) -> Result<ArrayRef, DataFusionError> {
 #[cfg(test)]
 mod test {
     use super::ContainsFunc;
+    use crate::expr_fn::contains;
     use arrow::array::{BooleanArray, StringArray};
     use arrow::datatypes::{DataType, Field};
     use datafusion_common::ScalarValue;
-    use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl};
+    use datafusion_expr::{ColumnarValue, Expr, ScalarFunctionArgs, ScalarUDFImpl};
     use std::sync::Arc;
 
     #[test]
@@ -186,4 +187,16 @@ mod test {
             *expect.into_array(2).unwrap()
         );
     }
+
+    #[test]
+    fn test_contains_api() {
+        let expr = contains(
+            Expr::Literal(ScalarValue::Utf8(Some("the quick brown fox".to_string()))),
+            Expr::Literal(ScalarValue::Utf8(Some("row".to_string()))),
+        );
+        assert_eq!(
+            expr.to_string(),
+            "contains(Utf8(\"the quick brown fox\"), Utf8(\"row\"))"
+        );
+    }
 }

datafusion/functions/src/string/mod.rs

@@ -140,7 +140,8 @@ pub mod expr_fn {
         "returns uuid v4 as a string value",
     ), (
         contains,
-        "Return true if search_string is found within string.",
+        "Return true if `search_string` is found within `string`.",
+        string search_string
     ));
 
     #[doc = "Removes all characters, spaces by default, from both sides of a string"]