docs(test): added readme for test

CONTRIBUTING.md

@@ -76,3 +76,7 @@ Just make sure you have thoroughly tested manually and pass shellcheck.
 
 If you are interested, checkout [here] to see how the unit test are implemented and
 use current unit tests as reference.
+
+## Finally
+
+Thanks for your interest in improving `dotbare`!

tests/README.md

@@ -0,0 +1,96 @@
+# Testing dotbare
+
+`dotbare` is unit tested using the [bats](https://github.com/bats-core/bats-core) testing
+frame work. Interaction with `fzf` are mocked using the PATH override method.
+
+Refer to bats homepage for usage of bats and their test basics.
+
+## Mocking
+
+One of the challenge when testing `dotbare` is interaction with `fzf`, `git` and some
+other shell functions. `fzf` is the most pain because it does require human interaction.
+
+Using the PATH override method, at the very least, we can assert if fzf is invoked with
+right arguments.
+
+### How it works
+
+There is a executable file called fzf in the test folder as well as git, tree etc. Before
+running test that requires fzf invokations, append the test folder path to the front of
+PATH variable.
+
+```sh
+#!/usr/bin/env bats
+
+stage_selected_dir() {
+  export PATH="${BATS_TEST_DIRNAME}:$PATH"
+  bash "${BATS_TEST_DIRNAME}"/../dotbare fadd --dir
+}
+```
+
+This way the executable will be executed by `dotbare` instead of the real `fzf`.
+
+### The fzf executable
+
+I'm sure there might be more elegant way of doing this, if you have suggestions please
+help me improve it. Currently for better readability in all the bats test file, I added
+bunch of `if` statement in the `fzf` executable to assert if `fzf` is being called
+correctly.
+
+```sh
+if [[ "$*" =~ '--multi --preview ' ]] && [[ "$*" =~ "tree -L 1 -C --dirsfirst {}" ]]; then
+  # dotbare fadd --dir -- "./fadd.bats" @test "fadd stage selected dir"
+  echo "fadd_stage_dir"
+fi
+```
+
+When the executable is being called, it will check for it's arguments and echo out a shorter
+word indicating the correct argument is passed.
+
+```sh
+#!/usr/bin/env bats
+
+@test "fadd stage selected dir" {
+  run stage_selected_dir
+  # we could assert if fzf is actually being invoked correctly
+  # in this case, it's supposed to search directory and using tree to provide preview
+  [[ "${output}" =~ "add fadd_stage_dir" ]]
+}
+```
+
+## Full example
+
+> You could always checkout more examples in tests folder
+
+The fzf executable
+
+```sh
+if [[ "$*" =~ '--header=select a commit' ]] && [[ "$*" =~ "show --color" ]]; then
+  # dotbare flog --reset -y -- "./flog.bats" @test "flog reset"
+  echo "--flog_reset"
+fi
+```
+
+The bats unit test file.
+
+```sh
+#!/usr/bin/env bats
+
+help() {
+  bash "${BATS_TEST_DIRNAME}"/../dotbare flog -h
+}
+reset() {
+  export PATH="${BATS_TEST_DIRNAME}:$PATH"
+  bash "${BATS_TEST_DIRNAME}"/../dotbare flog --reset -y
+}
+
+@test "flog help" {
+  run help
+  [ "${status}" -eq 0 ]
+  [ "${lines[0]}" = "Usage: dotbare flog [-h] [-r] [-R] [-e] [-c] [-y] ..." ]
+}
+@test "flog reset" {
+  run reset
+  [[ "${output}" =~ "reset --flog_reset" ]]
+}
+```