unit tests: add tests for get_grub_kernel_boot_parameter

This test suite makes use of three features provided by ShellSpec
 - funcion-based mock [2]: mock a function by re-defining and exporting it
 - parameterized tests [3]: run multiple sets of input against the same
   test
 - %text directive [4]: similar to heredoc but free of
   the indentation issue

Note
1. Describe and Context are aliases for ExampleGroup which a block for
grouping example groups or examples [5]. Describe and Context are used to
improve readability.
2. ShellSpec requires .shellspec file.

[1] https://github.com/dodie/testing-in-bash#detailed-comparision
[2] https://github.com/shellspec/shellspec#function-based-mock
[3] https://github.com/shellspec/shellspec#parameters---parameterized-example
[4] https://github.com/shellspec/shellspec#text---embedded-text
[5] https://github.com/shellspec/shellspec#dsl-syntax

Reviewed-by: Philipp Rudo <prudo@redhat.com>
Signed-off-by: Coiby Xu <coxu@redhat.com>

spec/kdumpctl_general_spec.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+Describe 'kdumpctl'
+	Include ./kdumpctl
+
+	Describe 'get_grub_kernel_boot_parameter()'
+		grubby() {
+			%text
+			#|index=1
+			#|kernel="/boot/vmlinuz-5.14.14-200.fc34.x86_64"
+			#|args="crashkernel=11M nvidia-drm.modeset=1 crashkernel=100M ro rhgb quiet crcrashkernel=200M crashkernel=32T-64T:128G,64T-102400T:180G fadump=on"
+			#|root="UUID=45fdf703-3966-401b-b8f7-cf056affd2b0"
+		}
+		DUMMY_PARAM=/boot/vmlinuz
+
+		Context "when given a kernel parameter in different positions"
+			# Test the following cases:
+			#  - the kernel parameter in the end
+			#  - the kernel parameter in the first
+			#  - the kernel parameter is crashkernel (suffix of crcrashkernel)
+			#  - the kernel parameter that does not exist
+			#  - the kernel parameter doesn't have a value
+			Parameters
+				# parameter          answer
+				fadump               on
+				nvidia-drm.modeset   1
+				crashkernel          32T-64T:128G,64T-102400T:180G
+				aaaa                 ""
+				ro                   ""
+			End
+
+			It 'should retrieve the value succesfully'
+				When call get_grub_kernel_boot_parameter "$DUMMY_PARAM" "$2"
+				The output should equal "$3"
+			End
+		End
+
+		It 'should retrive the last value if multiple <parameter=value> entries exist'
+			When call get_grub_kernel_boot_parameter "$DUMMY_PARAM" crashkernel
+			The output should equal '32T-64T:128G,64T-102400T:180G'
+		End
+
+		It 'should fail when called with kernel_path=ALL'
+			When call get_grub_kernel_boot_parameter ALL ro
+			The status should be failure
+			The error should include "kernel_path=ALL invalid"
+		End
+	End
+End