Applying tdd on select-only exercise

exercises/concept/intro-select/create_fixture.sql

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+DROP TABLE IF EXISTS weather_readings;
+CREATE TABLE weather_readings (
+  date        TEXT    NOT NULL,
+  location    TEXT    NOT NULL,
+  temperature REAL    NOT NULL,
+  humidity    INTEGER NOT NULL
+);
+
+.mode csv
+.import ./data.csv weather_readings

exercises/concept/intro-select/data.csv

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+"2025-10-22","Portland",53.1,72
+"2025-10-22","Seattle",56.2,66
+"2025-10-22","Boise",60.4,55
+"2025-10-23","Portland",54.6,70
+"2025-10-23","Seattle",57.8,68
+"2025-10-23","Boise",62.0,58

exercises/concept/intro-select/evaluate.py

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+from pathlib import Path
+import json
+import sys
+
+
+def gather_results(filename):
+    text = Path(filename).read_text()
+    list_start_indices = find_all_occurrences('[', text)
+    list_end_indices = find_all_occurrences(']', text)
+    return [
+        json.loads(text[begin:end+1])
+        for begin, end in zip(list_start_indices, list_end_indices)
+    ]
+
+
+def find_all_occurrences(char, string):
+    return [i for i, c, in enumerate(string) if c == char]
+
+
+def format_diff(expected, actual):
+    return ( 
+        f"\tExpected:\n"
+        f"\t\t{expected}\n"
+        f"\tActual:\n"
+        f"\t\t{actual}"
+    )
+
+def report_results(all_test_data, actual_results):
+    results = []
+    for test_data, actual in zip(all_test_data, actual_results):
+        result = {'description': test_data['description']}
+        if test_data['expected'] == actual:
+            result['status'] = 'pass'
+        else:
+            result['status'] = 'fail'
+            result['message'] = "Expected: " + json.dumps(test_data['expected'])
+            result['output'] = "Actual: " + json.dumps(actual)
+        results.append(result)
+    return make_result_report(results)
+
+
+def make_result_report(results):
+    status = 'pass' if all(r['status'] == 'pass' for r in results) else 'fail'
+    return {
+        "version": 3,
+        "status": status,
+        "tests": results
+    }
+
+
+def main():
+    test_data_filename, user_output_filename = sys.argv[1:3]
+    test_data = json.loads(Path(test_data_filename).read_text())
+    actual_results = gather_results(user_output_filename)
+    results = report_results(test_data, actual_results)
+    Path('results.json').write_text(json.dumps(results, indent=2))
+
+
+if __name__ == '__main__':
+    main()

exercises/concept/intro-select/intro-select.sql

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+SELECT * FROM weather_readings;
+
+SELECT location, temperature FROM weather_readings;
+
+-- This one will fail on purpose
+SELECT 'Hello, world.' AS say_hi;
+
+SELECT * FROM weather_readings WHERE location = 'Seattle';
+
+SELECT * FROM weather_readings WHERE humidity BETWEEN 60 AND 70;
+
+SELECT location FROM weather_readings;
+
+SELECT DISTINCT location FROM weather_readings;

exercises/concept/intro-select/intro-select_test.sql

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+-- Create database:
+.read ./create_fixture.sql
+
+.mode json
+
+-- Run user solution
+.output user_output.txt
+.read ./intro-select.sql
+
+-- Compare expected vs actual
+.shell python evaluate.py test_data.json user_output.txt

exercises/concept/intro-select/test_data.json

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+[
+    {
+        "description": "ALL records => SELECT * FROM weather_readings", 
+        "expected": [
+            {"date":"2025-10-22","location":"Portland","temperature":53.1,"humidity":72},
+            {"date":"2025-10-22","location":"Seattle","temperature":56.2,"humidity":66},
+            {"date":"2025-10-22","location":"Boise","temperature":60.4,"humidity":55},
+            {"date":"2025-10-23","location":"Portland","temperature":54.6,"humidity":70},
+            {"date":"2025-10-23","location":"Seattle","temperature":57.79999999999999,"humidity":68},
+            {"date":"2025-10-23","location":"Boise","temperature":62.0,"humidity":58}
+        ]
+    },
+    {
+        "description": "Just location and temperature columns => SELECT location, temperature FROM weather_readings",
+        "expected": [
+            {"location":"Portland","temperature":53.1},
+            {"location":"Seattle","temperature":56.2},
+            {"location":"Boise","temperature":60.4},
+            {"location":"Portland","temperature":54.6},
+            {"location":"Seattle","temperature":57.79999999999999},
+            {"location":"Boise","temperature":62.0}
+        ]
+    },
+    {
+        "description": "Without \"FROM\" => SELECT 'Hello, world.'",
+        "expected": [
+            {"'Hello, world.'":"Hello, world."}
+        ]
+    },
+    {
+        "description": "All records from Seatle location => SELECT * FROM weather_readings WHERE location = 'Seattle'",
+        "expected": [
+            {"date":"2025-10-22","location":"Seattle","temperature":56.2,"humidity":66},
+            {"date":"2025-10-23","location":"Seattle","temperature":57.79999999999999,"humidity":68}
+        ]
+    },
+        {
+        "description": "All records where humidity in range => SELECT * FROM weather_readings WHERE humidity BETWEEN 60 AND 70",
+        "expected": [
+            {"date":"2025-10-22","location":"Seattle","temperature":56.2,"humidity":66},
+            {"date":"2025-10-23","location":"Portland","temperature":54.6,"humidity":70},
+            {"date":"2025-10-23","location":"Seattle","temperature":57.79999999999999,"humidity":68}
+        ]
+    },
+    {
+        "description": "Just location column => SELECT location FROM weather_readings",
+        "expected": [
+            {"location":"Portland"},
+            {"location":"Seattle"},
+            {"location":"Boise"},
+            {"location":"Portland"},
+            {"location":"Seattle"},
+            {"location":"Boise"}
+        ]
+    },
+    {
+        "description": "Only unique locations => SELECT DISTINCT location FROM weather_readings",
+        "expected": [
+            {"location":"Portland"},
+            {"location":"Seattle"},
+            {"location":"Boise"}
+        ]
+    }
+]