Add CONTRIBUTING.md (#80)

Signed-off-by: Yu Ishikawa <[email protected]>

CONTRIBUTING.md

@@ -0,0 +1,84 @@
+# Contributing to dbt_data_privacy
+
+Thank you for your interest in contributing to dbt_data_privacy!
+
+## Before you start
+
+We utilize a unique approach to implement unit testing for dbt packages.
+This approach is necessary because Jinja2 does not inherently support unit testing.
+The dbt Developer Blog provides an excellent article on implementing unit testing for dbt packages.
+This article serves as a valuable resource for understanding the concept of unit testing within the context of dbt packages.
+
+[An introduction to unit testing your dbt Packages \| dbt Developer Blog](https://docs.getdbt.com/blog/unit-testing-dbt-packages)
+
+Unit testing becomes increasingly crucial as a dbt package grows in complexity, ensuring that the package functions as intended.
+
+## How to develop
+
+### Directory structure
+
+We primarily utilize the following directories for developing the dbt package.
+The `macros/` directory houses the core logic of dbt_data_privacy in the form of dbt Macros.
+The `integration_tests/` directory contains test files for both unit and integration testing.
+
+- `macros/`: Contains the dbt Macros that constitute dbt_data_privacy.
+- `integration_tests/`: Houses integration tests for dbt_data_privacy, encompassing both unit and integration tests.
+
+### How to set up the development environment
+
+Begin by cloning the repository to your local machine.
+Navigate to the `integration_tests/` directory to execute unit and integration tests.
+The [./integration_tests/Makefile](./integration_tests/Makefile) provides a set of helpful commands.
+The `make setup` command installs dependencies and configures the development environment.
+
+```shell
+cd dbt_data_privacy/integration_tests
+
+# Install dependencies
+make setup
+```
+
+### How to run unit testing
+
+A dedicated Makefile target is available for running unit tests.
+This target allows you to run unit tests with a specified target and a vars file.
+
+```shell
+make run-unit-tests
+```
+
+Note that unit testing cannot be parallelized due to the sequential nature of test execution.
+If an error occurs in a test file, the unit testing process halts and returns an error.
+Consequently, it is not possible to capture all failed tests in a single command.
+
+### How to implement unit tests
+
+When adding or modifying dbt Macros in the `macros/` directory, it is essential to implement corresponding unit tests.
+Place the test file in the `integration_tests/macros/` directory.
+
+For example, the dbt Macro located at [macros/codegen/generate_privacy_protected_model_sql.sql](macros/codegen/generate_privacy_protected_model_sql.sql) is responsible for generating a secured dbt Model.
+The corresponding unit test for this macro can be found at [integration_tests/macros/tests/codegen/test_generate_privacy_protected_model_sql.sql](integration_tests/macros/tests/codegen/test_generate_privacy_protected_model_sql.sql).
+This illustrates the convention of placing a dbt Macro and its associated unit test file in a structured manner.
+
+Custom dbt Macros, such as `assert_equals`, are available in the [integration_tests/macros/test_utils/](integration_tests/macros/test_utils/) directory to facilitate effective unit testing of dbt Macros.
+Leverage these macros to create more comprehensive and robust unit tests.
+
+### How to run integration testing
+
+In addition to unit testing, we also perform integration testing for dbt_data_privacy.
+This involves building dbt models, including secured models generated by the dbt_data_privacy package, on a data warehouse such as BigQuery.
+
+1. Generate secured models using the provided command.
+2. Compile the dbt Models to ensure the generated secured models are valid.
+3. Execute a `dbt build` command to thoroughly test the generated models.
+
+```shell
+# 1. Generate secured models
+make generate
+
+# 2. Compile dbt Models if generated secured models are valid
+make compile
+
+# 2. Run a `dbt build` command to test generated models
+make run-integration-tests
+```