Contessa

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- Fix project metadata
- Fix return consistency results, add test

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- Format code with Black
- Fix Travis deployment
- Add run_only methods

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- remove `use_prefix` for result_table. User can't change name of the table
- remove Enum for Checks. Prefix of the table is in `_table_prefix` attribute on models
- change migration template. do migration for all the models separately if needed
- refactor migration tests. introduce MigrationTestCase class.
- updates of the quality checks are now possible. you can rerun same check and it will be updated.
- improvements to consistency checker:
- add time filter
- fix comparison of tables when they store rows in different order
- allow to compare subset of columns
- allow custom query for selecting results from table

*Migration needed*
- add new migration. Add nullables + default time_filter ('not_set') for QualityCheck and
ConsistencyCheck models. Run this command:
`contessa-migrate -u $DB_URI -s data_quality -v 0.2.5`


Note we're setting nullables for columns bellow. Make sure you don't have null values in them.

*QualityCheck*
- rule_type
- rule_name
- attribute
- time_filter (fix with 1. step)

*ConsistencyCheck*
- type
- name
- left_table
- right_table
- time_filter (fix with 1. step)

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- *breaking change* - output data schema change - name renamed to type, added name. Do the :ref:`migration` before use this version.
- refactor rules to use jinja2 as templating system
- allow to configure time interval in `time_filter`
- add docs - https://contessa.readthedocs.io/en/latest/
- add debug sql prints for rules
- add BigQuery support
- add ConsistencyChecker, supports rowcount comparison
- add "column" to CustomSQLRule. will be saved in quality check as "attribute"

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- rules description is mandatory and can be used in all rules

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- `condition` parameter in SqlRule is templated now