Issue 1075: Add refactored ETL tests to NRI (#1088)

* Adds a substantially refactored ETL test to the National Risk Index, to be used as a model for other tests

data/data-pipeline/data_pipeline/tests/sources/example/etl.py

@@ -0,0 +1,56 @@
+import zipfile
+import pandas as pd
+
+from data_pipeline.config import settings
+from data_pipeline.etl.base import ExtractTransformLoad, ValidGeoLevel
+from data_pipeline.utils import get_module_logger
+
+logger = get_module_logger(__name__)
+
+
+class ExampleETL(ExtractTransformLoad):
+    """A test-only, simple implementation of the ETL base class.
+
+    This can be used for the base tests of the `TestETL` class.
+    """
+
+    INPUT_FIELD_NAME = "Input Field 1"
+    EXAMPLE_FIELD_NAME = "Example Field 1"
+
+    NAME = "example_dataset"
+    LAST_UPDATED_YEAR = 2017
+    SOURCE_URL = "https://www.example.com/example.zip"
+    GEO_LEVEL = ValidGeoLevel.CENSUS_TRACT
+
+    def __init__(self):
+        self.COLUMNS_TO_KEEP = [
+            self.GEOID_TRACT_FIELD_NAME,
+            self.EXAMPLE_FIELD_NAME,
+        ]
+
+    def extract(self):
+        # Pretend to download zip from external URL, write it to CSV.
+        zip_file_path = (
+            settings.APP_ROOT
+            / "tests"
+            / "sources"
+            / "example"
+            / "data"
+            / "input.zip"
+        )
+
+        logger.info(f"Extracting {zip_file_path}")
+        with zipfile.ZipFile(zip_file_path, "r") as zip_ref:
+            zip_ref.extractall(self.TMP_PATH)
+
+    def transform(self):
+        logger.info(f"Loading file from {self.TMP_PATH / 'input.csv'}.")
+        df: pd.DataFrame = pd.read_csv(
+            self.TMP_PATH / "input.csv",
+            dtype={self.GEOID_TRACT_FIELD_NAME: "string"},
+            low_memory=False,
+        )
+
+        df[self.EXAMPLE_FIELD_NAME] = df[self.INPUT_FIELD_NAME] * 2
+
+        self.output_df = df