feat: extract MemTable to ease testing (#133)

* feat: memtable backed by DataFusion to ease testing

* move test utility codes out of src folder

* Implement our own MemTable because DataFusion's MemTable does not support limit; and replace the original testing numbers table.

* fix: address PR comments

* fix: "testutil" -> "test-util"

* roll back "NumbersTable"

Co-authored-by: luofucong <luofucong@greptime.com>

src/table/src/error.rs

@@ -36,14 +36,27 @@ pub enum InnerError {
         source: ArrowError,
         backtrace: Backtrace,
     },
+
+    #[snafu(display("Failed to convert Arrow schema, source: {}", source))]
+    SchemaConversion {
+        source: datatypes::error::Error,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display("Table projection error, source: {}", source))]
+    TableProjection {
+        source: ArrowError,
+        backtrace: Backtrace,
+    },
 }
 
 impl ErrorExt for InnerError {
     fn status_code(&self) -> StatusCode {
         match self {
-            InnerError::Datafusion { .. } | InnerError::PollStream { .. } => {
-                StatusCode::EngineExecuteQuery
-            }
+            InnerError::Datafusion { .. }
+            | InnerError::PollStream { .. }
+            | InnerError::SchemaConversion { .. }
+            | InnerError::TableProjection { .. } => StatusCode::EngineExecuteQuery,
             InnerError::MissingColumn { .. } => StatusCode::InvalidArguments,
             InnerError::ExecuteRepeatedly { .. } => StatusCode::Unexpected,
         }

src/table/src/table/adapter.rs

@@ -25,8 +25,8 @@ use datafusion::physical_plan::{
 };
 use datafusion_common::record_batch::RecordBatch as DfRecordBatch;
 use datatypes::arrow::error::{ArrowError, Result as ArrowResult};
-use datatypes::schema::SchemaRef as TableSchemaRef;
 use datatypes::schema::SchemaRef;
+use datatypes::schema::{Schema, SchemaRef as TableSchemaRef};
 use futures::Stream;
 use snafu::prelude::*;
 
@@ -215,10 +215,7 @@ impl Table for TableAdapter {
             .await
             .context(error::DatafusionSnafu)?;
 
-        Ok(Box::pin(RecordBatchStreamAdapter::new(
-            self.schema.clone(),
-            df_stream,
-        )))
+        Ok(Box::pin(RecordBatchStreamAdapter::try_new(df_stream)?))
     }
 
     fn supports_filter_pushdown(&self, filter: &Expr) -> Result<FilterPushDownType> {
@@ -278,8 +275,10 @@ pub struct RecordBatchStreamAdapter {
 }
 
 impl RecordBatchStreamAdapter {
-    pub fn new(schema: SchemaRef, stream: DfSendableRecordBatchStream) -> Self {
-        Self { schema, stream }
+    pub fn try_new(stream: DfSendableRecordBatchStream) -> Result<Self> {
+        let schema =
+            Arc::new(Schema::try_from(stream.schema()).context(error::SchemaConversionSnafu)?);
+        Ok(Self { schema, stream })
     }
 }