Applying TDD on SELECT - Proof of Concept (disposable draft)

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/create_test_table.sql

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+DROP TABLE IF EXISTS tests;
+CREATE TABLE IF NOT EXISTS tests (
+  description TEXT NOT NULL,
+  -- The following section is needed by the online test-runner
+  status TEXT DEFAULT 'fail',
+  message TEXT,
+  output TEXT,
+  test_code TEXT,
+  task_id INTEGER DEFAULT NULL,
+  -- Here are columns for the actual tests
+  expected TEXT NOT NULL
+);
+
+INSERT INTO tests (description, expected)
+VALUES
+  ('ALL records => SELECT * FROM weather_readings', '[{"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":57.8,"humidity":68},{"date":"2025-10-23","location":"Boise","temperature":62.0,"humidity":58}]'),
+  ('Just location and temperature columns => SELECT location, temperature FROM weather_readings', '[{"location":"Portland","temperature":53.1},{"location":"Seattle","temperature":56.2},{"location":"Boise","temperature":60.4},{"location":"Portland","temperature":54.6},{"location":"Seattle","temperature":57.8},{"location":"Boise","temperature":62.0}]'),
+  ('Without "FROM" => SELECT ''Hello, world.''', '[{"''Hello, world.''":"Hello, world."}]'),
+  ('All records from Seatle location => SELECT * FROM weather_readings WHERE location = ''Seattle''', '[{"date":"2025-10-22","location":"Seattle","temperature":56.2,"humidity":66},{"date":"2025-10-23","location":"Seattle","temperature":57.8,"humidity":68}]'),
+  ('All records where humity in range => SELECT * FROM weather_readings WHERE humidity BETWEEN 60 AND 70', '[{"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":57.8,"humidity":68}]'),
+  ('Just location column => SELECT location FROM weather_readings', '[{"location":"Portland"},{"location":"Seattle"},{"location":"Boise"},{"location":"Portland"},{"location":"Seattle"},{"location":"Boise"}]'),
+  ('Only unique locations => SELECT DISTINCT location FROM weather_readings', '[{"location":"Portland"},{"location":"Seattle"},{"location":"Boise"}]');
+;

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/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
+-- Read user student solution and save any output as markdown in user_output.md:
+.mode markdown
+.output user_output.md
+.echo on  
+.read ./intro-select.sql
+.echo off
+.output
+.shell sed -i 1d user_output.md
+
+-- Re-run stub file to collect the results as json arrays
+.mode json
+.output outputs.txt
+.read ./intro-select.sql
+.output
+-- Creating the results table from the outputs.txt file
+DROP TABLE IF EXISTS outputs;
+CREATE TEMPORARY TABLE outputs (line TEXT NOT NULL);
+.mode tabs
+.import ./outputs.txt outputs
+DROP TABLE IF EXISTS results;
+CREATE TABLE results (result TEXT NOT NULL);
+WITH inputs (input) AS (
+  SELECT JSON(PRINTF('[%s]', GROUP_CONCAT(RTRIM(TRIM(line), ','), ',')))
+    FROM outputs
+)
+INSERT INTO results (result)
+SELECT j.value
+  FROM inputs, JSON_EACH(input) j
+;
+
+-- Create a clean testing environment:
+.read ./create_test_table.sql
+-- Comparison of user input and the tests updates the status for each test:
+UPDATE tests
+   SET status = 'pass'
+  FROM (SELECT result FROM results) AS actual
+ WHERE NOT EXISTS (
+   SELECT key, value, type, path
+     FROM JSON_TREE(result)
+    WHERE type NOT IN ('array', 'object')
+   EXCEPT
+   SELECT key, value, type, path
+     FROM JSON_TREE(expected)
+    WHERE type NOT IN ('array', 'object')
+ )
+  AND NOT EXISTS (
+    SELECT key, value, type, path
+      FROM JSON_TREE(expected)
+     WHERE type NOT IN ('array', 'object')
+    EXCEPT
+    SELECT key, value, type, path
+      FROM JSON_TREE(result)
+     WHERE type NOT IN ('array', 'object')
+  )
+;
+
+-- Update message for failed tests to give helpful information:
+UPDATE tests
+  -- SET message = 'Result for "' || tests.description || '"' || ' is <' || COALESCE(actual.result, 'NULL') || '> but should be <' || tests.expected || '>'
+  SET message = 'Result for <"' || tests.description || '">' || ' NOT FOUND' -- need improvements
+WHERE tests.status = 'fail';
+
+-- Save results to ./output.json (needed by the online test-runner)
+.mode json
+.once './output.json'
+SELECT
+  description,
+  status,
+  message,
+  output,
+  test_code,
+  task_id
+FROM
+  tests;
+
+-- Display test results in readable form for the student:
+.mode table
+SELECT
+  description,
+  status,
+  message
+FROM
+  tests;

exercises/concept/intro-select/outputs.txt

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+[{"date":"2025-10-22","location":"Portland","temperature":53.10000000000000142,"humidity":72},
+{"date":"2025-10-22","location":"Seattle","temperature":56.20000000000000284,"humidity":66},
+{"date":"2025-10-22","location":"Boise","temperature":60.39999999999999858,"humidity":55},
+{"date":"2025-10-23","location":"Portland","temperature":54.60000000000000142,"humidity":70},
+{"date":"2025-10-23","location":"Seattle","temperature":57.79999999999999716,"humidity":68},
+{"date":"2025-10-23","location":"Boise","temperature":62.0,"humidity":58}]
+[{"location":"Portland","temperature":53.10000000000000142},
+{"location":"Seattle","temperature":56.20000000000000284},
+{"location":"Boise","temperature":60.39999999999999858},
+{"location":"Portland","temperature":54.60000000000000142},
+{"location":"Seattle","temperature":57.79999999999999716},
+{"location":"Boise","temperature":62.0}]
+[{"say_hi":"Hello, world."}]
+[{"date":"2025-10-22","location":"Seattle","temperature":56.20000000000000284,"humidity":66},
+{"date":"2025-10-23","location":"Seattle","temperature":57.79999999999999716,"humidity":68}]
+[{"date":"2025-10-22","location":"Seattle","temperature":56.20000000000000284,"humidity":66},
+{"date":"2025-10-23","location":"Portland","temperature":54.60000000000000142,"humidity":70},
+{"date":"2025-10-23","location":"Seattle","temperature":57.79999999999999716,"humidity":68}]
+[{"location":"Portland"},
+{"location":"Seattle"},
+{"location":"Boise"},
+{"location":"Portland"},
+{"location":"Seattle"},
+{"location":"Boise"}]
+[{"location":"Portland"},
+{"location":"Seattle"},
+{"location":"Boise"}]