When Test Cases are exported in CSV format, the test step data gets exported along with Test Cases in a Pivot Table format, like

TC - Id	.... ...	TS - Id	TS - Sequence Number	TS - Action	TS - Expected Results	TS - Custom Field 1	TS - Custom Field 2

While importing this data into a project:

If TC - Id OR TC - External Id is not mapped, then
- the Test Steps cannot be imported.
If TC-ID/External-ID is mapped and a TC-ID/External-ID already exist, and

- if TS-ID is mapped and
  - if TS-ID column is left blank in the CSV file and other fields have been entered, then a new Test Step(TS-ID) is created against this TC-ID/External-ID.
  - if TS-ID already exists, then the data is updated.
  - if TS-ID doesn’t exists, then an error will be generated.
- if TS-ID is not mapped,
- - the existing test steps will be retained and new test steps (specified in the CSV file) will be created.
Sequence number may not be mapped to the target, it will be auto-generated.
Rest of the fields may or may not be mapped, depending on the user's choice. These include
- TS - Action
- TS - Expected Results
- TS - Custom Fields

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