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Columns with time-based datatypes can be edited by clicking the drop-down selector in each cell.
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Authoring, intercepting, or uploading large volumes of test data will eventually prevent those data from being interactively edited using MettleCI Workbench’s Unit Test Editor. In these circumstances you will be presented with a message of the form:
{data-file-name}.csv is in ReadOnly mode. The data file is larger than is recommended for editing in workbench.
In this instance you can still edit the data file by exporting it to a CSV file (using the download button on the Unit Test Editor toolbar), editing it using your favourite local CSV editor, such as Microsoft Excel, and then re-importing it using the upload button.