First draft of adding tests for empty join filters

Author: tschwarzinger

datafusion/expr/src/logical_plan/builder.rs

@@ -2195,6 +2195,40 @@ mod tests {
         );
     }
 
+    #[test]
+    fn plan_builder_join_cannot_accidentally_create_cross_join() {
+        let schema = employee_schema();
+        let lhs = LogicalPlanBuilder::scan("lhs", table_source(&schema), projection);
+        let rhs = LogicalPlanBuilder::scan("rhs", table_source(&schema), projection)
+            .build()
+            .unwrap();
+
+        let join = lhs
+            .join(JoinType::Inner, &rhs, (vec![], vec![]), None)
+            .unwrap_err();
+
+        assert_eq!(
+            err.strip_backtrace(),
+            "Error during planning: table_name cannot be empty"
+        );
+    }
+
+    #[test]
+    fn plan_builder_join_no_filter_is_ok_for_non_inner_join() {
+        let schema = employee_schema();
+        let lhs = LogicalPlanBuilder::scan("lhs", table_source(&schema), projection);
+        let rhs = LogicalPlanBuilder::scan("rhs", table_source(&schema), projection)
+            .build()
+            .unwrap();
+
+        let join = lhs.join(JoinType::Left, &rhs, (vec![], vec![]), None);
+
+        assert!(
+            join.is_ok(),
+            "A non-inner join without a filter should be allowed"
+        );
+    }
+
     #[test]
     fn plan_builder_sort() -> Result<()> {
         let plan =