Added bats container and makefile for bats testing

.github/tests/bats/Dockerfile

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+FROM bats/bats:latest
+RUN apk add git
+RUN mkdir /opt/bats-test-helpers
+RUN git clone https://github.com/ztombol/bats-support /opt/bats-test-helpers/bats-support
+RUN git clone https://github.com/ztombol/bats-assert /opt/bats-test-helpers/bats-assert
+RUN git clone https://github.com/lox/bats-mock /opt/bats-test-helpers/lox-bats-mock
+WORKDIR /code/

.github/tests/bats/README.md

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+# bats
+
+This folder contains the test harness for testing bash scripts.
+
+Inspired from :  [Marck Oemar's Medium post](https://marck-oemar.medium.com/unusual-unit-testing-part-1-bash-scripts-with-bats-55ac78e61491)

Makefile

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+build_bats:
+	docker build .github/tests/bats -t bats-with-helpers:latest
+
+test_bashscripts: build_bats
+	docker run --rm -v "${PWD}/.github:/code" bats-with-helpers:latest /code/tests/