code: def test_str_expr(
      default_expr_renderer: DefaultSqlExpressionRenderer,
  ) -> None:  # noqa: D
      actual = default_expr_renderer.render_sql_expr(
          SqlStringExpression("a + b")
      ).sql
      expected = "a + b"
      assert actual == expected
  
imports: from __future__ import annotations
  import logging
  import textwrap
  import pytest
  from dbt_semantic_interfaces.type_enums.date_part import DatePart
  from dbt_semantic_interfaces.type_enums.time_granularity import TimeGranularity
  from metricflow.sql.render.expr_renderer import DefaultSqlExpressionRenderer
  from metricflow.sql.sql_exprs import SqlAggregateFunctionExpression, SqlBetweenExpression, SqlCastToTimestampExpression, SqlColumnReference, SqlColumnReferenceExpression, SqlColumnReplacements, SqlComparison, SqlComparisonExpression, SqlDateTruncExpression, SqlExtractExpression, SqlFunction, SqlIsNullExpression, SqlLogicalExpression, SqlLogicalOperator, SqlNullExpression, SqlRatioComputationExpression, SqlStringExpression, SqlStringLiteralExpression, SqlWindowFunction, SqlWindowFunctionExpression, SqlWindowOrderByArgument
label_desc: Use image node_id 2 for calling a global function with example usage: test_str_expr(default_expr_renderer) without return types