improve docs

Author: alamb

datafusion/optimizer/src/optimizer.rs

@@ -531,8 +531,22 @@ mod tests {
             "Optimizer rule 'get table_scan rule' failed\n\
             caused by\nget table_scan rule\ncaused by\n\
             Internal error: Failed due to a difference in schemas, \
-            original schema: DFSchema { inner: Schema { fields: [], metadata: {} }, field_qualifiers: [], functional_dependencies: FunctionalDependencies { deps: [] } }, \
-            new schema: DFSchema { inner: Schema { fields: [Field { name: \"a\", data_type: UInt32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: \"b\", data_type: UInt32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: \"c\", data_type: UInt32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }], metadata: {} }, field_qualifiers: [Some(Bare { table: \"test\" }), Some(Bare { table: \"test\" }), Some(Bare { table: \"test\" })], functional_dependencies: FunctionalDependencies { deps: [] } }.\nThis was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker",
+            original schema: DFSchema { inner: Schema { \
+            fields: [], \
+            metadata: {} }, \
+            field_qualifiers: [], \
+            functional_dependencies: FunctionalDependencies { deps: [] } \
+            }, \
+            new schema: DFSchema { inner: Schema { \
+            fields: [\
+              Field { name: \"a\", data_type: UInt32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }, \
+              Field { name: \"b\", data_type: UInt32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }, \
+              Field { name: \"c\", data_type: UInt32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }\
+            ], \
+            metadata: {} }, \
+            field_qualifiers: [Some(Bare { table: \"test\" }), Some(Bare { table: \"test\" }), Some(Bare { table: \"test\" })], \
+            functional_dependencies: FunctionalDependencies { deps: [] } }.\n\
+            This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker",
             err.strip_backtrace()
         );
     }