Test for export button widget

[codecov[bot]]

Codecov Report

Patch coverage: 95.23% and project coverage change: +3.84 :tada:

Comparison is base (85f811e) 72.75% compared to head (7fd07e2) 76.59%.

:exclamation: Current head 7fd07e2 differs from pull request most recent head 3fda300. Consider uploading reports for the commit 3fda300 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #469 +/- ## ========================================== + Coverage 72.75% 76.59% +3.84% ========================================== Files 23 25 +2 Lines 3516 3606 +90 ========================================== + Hits 2558 2762 +204 + Misses 958 844 -114 ``` | Flag | Coverage Δ | | |---|---|---| | python-3.10 | `76.59% <95.23%> (+3.84%)` | :arrow_up: | | python-3.8 | `76.65% <95.23%> (+3.84%)` | :arrow_up: | | python-3.9 | `76.65% <95.23%> (+3.84%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/aiidalab/aiidalab-widgets-base/pull/469?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab) | Coverage Δ | | |---|---|---| | [aiidalab\_widgets\_base/elns.py](https://codecov.io/gh/aiidalab/aiidalab-widgets-base/pull/469?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#diff-YWlpZGFsYWJfd2lkZ2V0c19iYXNlL2VsbnMucHk=) | `77.38% <75.00%> (+58.33%)` | :arrow_up: | | [tests/conftest.py](https://codecov.io/gh/aiidalab/aiidalab-widgets-base/pull/469?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#diff-dGVzdHMvY29uZnRlc3QucHk=) | `78.23% <88.88%> (+2.01%)` | :arrow_up: | | [aiidalab\_widgets\_base/\_\_init\_\_.py](https://codecov.io/gh/aiidalab/aiidalab-widgets-base/pull/469?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#diff-YWlpZGFsYWJfd2lkZ2V0c19iYXNlL19faW5pdF9fLnB5) | `100.00% <100.00%> (ø)` | | | [aiidalab\_widgets\_base/export.py](https://codecov.io/gh/aiidalab/aiidalab-widgets-base/pull/469?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#diff-YWlpZGFsYWJfd2lkZ2V0c19iYXNlL2V4cG9ydC5weQ==) | `100.00% <100.00%> (+76.00%)` | :arrow_up: | | [tests/test\_elns.py](https://codecov.io/gh/aiidalab/aiidalab-widgets-base/pull/469?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#diff-dGVzdHMvdGVzdF9lbG5zLnB5) | `100.00% <100.00%> (ø)` | | | [tests/test\_export.py](https://codecov.io/gh/aiidalab/aiidalab-widgets-base/pull/469?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab#diff-dGVzdHMvdGVzdF9leHBvcnQucHk=) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidalab)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.