# Testing expressions

You test your expression to check that results are as expected. The following figure is an example of an expression that has been evaluated and tested.

Information note

Testing an expression that contains an analytic function will validate the syntax without actually executing the function. Additionally, the test will only be performed on a single record.

Information note

Compose does not check the data types of columns used in an expression for compatibility. For example, if a column of type integer is used in an expression for a column of type varchar, the expression will not be executed successfully.

##### Test Expression

![](https://help.qlik.com/en-US/compose/December2024/Content/Resources/Images/ComposeForDataLakes/testExpress_result.png)

To test an expression:

1. In the Expression Builder window, build an expression as described in [Building Expressions](https://help.qlik.com/en-US/compose/December2024/Content/ComposeDWDL/Main/DL/Model/tasks_buildExpress.htm).

2. Click **Parse Expression** as described in [Parsing expressions](https://help.qlik.com/en-US/compose/December2024/Content/ComposeDWDL/Main/DL/Model/tasks_evalExpression.htm).

3. View the parameters that are displayed. If your expression is not valid, an error message is displayed.

4. Optionally edit the parameters name(s) as described in [Editing parameter names](https://help.qlik.com/en-US/compose/December2024/Content/ComposeDWDL/Main/DL/Model/edit_parameter_names.htm).

5. Type values for each parameter and then click **Test Expression** to see the expression result.

   For example, using the expression in [Test Expression](https://help.qlik.com/en-US/compose/December2024/Content/ComposeDWDL/Main/DL/Model/tasks_testExpress.htm#ar_model_1701435085_beibehjd), type `Mike` for `FirstName` and `Smith` for `LastName`. The result displayed is `Mike Smith`.

6. This step is only available for transformations created in the **Edit Mappings** window. When you create a transformation in the **Edit Mappings** window, an additional button called **Show Data** appears to the left of the **Test Expression** button. You can click this button to see how your expression translates into actual data.

   For example, clicking the **Show Data** button for the expression `UnitPrice*Quantity` will open the following window.

   ![](https://help.qlik.com/en-US/compose/December2024/Content/Resources/Images/ComposeForDataLakes/show_data.png)

   For more information on the **Edit Mappings** window, see [Column mappings](https://help.qlik.com/en-US/compose/December2024/Content/ComposeDWDL/Main/DL/Storage%20Zone/edit_column_mappings_hive.htm) in [Creating and Managing Storage Zone Tasks](https://help.qlik.com/en-US/compose/December2024/Content/ComposeDWDL/Main/DL/Storage%20Zone/create_and_manage_data_warehouse.htm).