PL/pg SQL: add pgTAP test framework support

plpgsql/README.md

@@ -9,19 +9,33 @@ To use remote / local dockerized database, add ``` --host --port --username```
 In shell:
 - create database: ```createdb gilded_rose```
 - create item table (structure): ```psql -d gilded_rose -f ./structure/create.sql``` 
-- load code into database: ```psql -d gilded_rose -f ./code/update_quality.sql ```
+- load code into database: ```psql -d gilded_rose -f ./src/update_quality.sql ```
 
 If you get this message```LINE 1: CREATE OR REPLACE PROCEDURE public.update_quality()```, your PostgreSQL version may under 11, consider upgrading.
 
-# Interactive run
+# Run 
 In shell:
-- load test data into database: ```psql -d gilded_rose -f ./test/data/load.sql```
+- load manual test data into database: ```psql -d gilded_rose -f ./test/manual/load.sql```
 - connect to CLI: ```psql -d gilded_rose```
 - check item state: ```SELECT * FROM item;```
 - execute item update: ```CALL update_quality();```
 - check item state: ```SELECT * FROM item;```
+- empty table : ```TRUNCATE TABLE item;```
+
 
 # Test
-No test code provided, only a sample of test data
-TODO: [https://pgtap.org/](introduce TAP - xUnit for PL/pg SQL)
 
+## Using pgTAP
+
+### Requirements
+Install pgTAP [instructions here](https://pgtap.org/documentation.html#installation)
+
+```item``` table is supposed to be empty. 
+If not, it would cause a (false positive)[https://en.wikipedia.org/wiki/False_positives_and_false_negatives]
+
+### Execute
+In shell, execute ```pg_prove --dbname gilded_rose test/pgtap/*.sql```. 
+You should get ```test/pgtap/template.sql .. ok All tests successful.```
+
+If you get this message ```ERROR: function plan(integer) does not exist LINE 1: SELECT PLAN(1);```, pgTAP is not working => check your pgTAP installation. 
+If you get this message ```Failed test:  2 Parse errors: Bad plan.  You planned 1 tests but ran 2.```, the item table contains data, interfering with the test => empty it, then run test again.