test(cubesql): Implement mock TransportService::load for TestConnectionTransport (#8560)

Add TestContext to hold all necessary test harness
Intention is to set up mock cube responses during test between text context init and query execution

Lift TestConnectionTransport to module level and store it in TestContext

Add simple mocks for TransportService::load to TestConnectionTransport, and use it for simple test

Author: mcheshkov

rust/cubesql/cubesql/src/compile/mod.rs

@@ -1334,6 +1334,7 @@ mod tests {
     use chrono::Datelike;
     use cubeclient::models::{
         V1LoadRequestQuery, V1LoadRequestQueryFilterItem, V1LoadRequestQueryTimeDimension,
+        V1LoadResponse, V1LoadResult, V1LoadResultAnnotation,
     };
     use pretty_assertions::assert_eq;
     use regex::Regex;
@@ -1357,7 +1358,7 @@ mod tests {
     use crate::compile::test::{
         convert_select_to_query_plan, convert_select_to_query_plan_customized,
         convert_select_to_query_plan_with_config, convert_select_to_query_plan_with_meta,
-        execute_queries_with_flags, execute_query, init_testing_logger,
+        execute_queries_with_flags, execute_query, init_testing_logger, TestContext,
     };
 
     #[tokio::test]
@@ -16451,6 +16452,61 @@ ORDER BY "source"."str0" ASC
             .contains("EXTRACT"));
     }
 
+    // TODO using this is not correct, but works for now
+    fn empty_annotation() -> V1LoadResultAnnotation {
+        V1LoadResultAnnotation::new(json!([]), json!([]), json!([]), json!([]))
+    }
+
+    fn simple_load_response(data: Vec<serde_json::Value>) -> V1LoadResponse {
+        V1LoadResponse::new(vec![V1LoadResult::new(empty_annotation(), data)])
+    }
+
+    #[tokio::test]
+    async fn test_cube_scan_exec() {
+        init_testing_logger();
+
+        let context = TestContext::new(DatabaseProtocol::PostgreSQL).await;
+
+        // language=PostgreSQL
+        let query = r#"
+            SELECT dim_str0
+            FROM MultiTypeCube
+            GROUP BY 1
+        "#;
+
+        let expected_cube_scan = V1LoadRequestQuery {
+            measures: Some(vec![]),
+            segments: Some(vec![]),
+            dimensions: Some(vec!["MultiTypeCube.dim_str0".to_string()]),
+            time_dimensions: None,
+            order: None,
+            limit: None,
+            offset: None,
+            filters: None,
+            ungrouped: None,
+        };
+
+        assert_eq!(
+            context
+                .convert_sql_to_cube_query(query)
+                .await
+                .unwrap()
+                .as_logical_plan()
+                .find_cube_scan()
+                .request,
+            expected_cube_scan,
+        );
+
+        context
+            .add_cube_load_mock(
+                expected_cube_scan,
+                simple_load_response(vec![json!({"MultiTypeCube.dim_str0": "foo"})]),
+            )
+            .await;
+
+        insta::assert_snapshot!(context.execute_query(query).await.unwrap());
+    }
+
     #[tokio::test]
     async fn test_wrapper_tableau_week_number() {
         if !Rewriter::sql_push_down_enabled() {

rust/cubesql/cubesql/src/compile/snapshots/cubesql__compile__tests__cube_scan_exec.snap

@@ -0,0 +1,9 @@
+---
+source: cubesql/src/compile/mod.rs
+expression: context.execute_query(query).await.unwrap()
+---
++----------+
+| dim_str0 |
++----------+
+| foo      |
++----------+