t/: Move `$BIN` variable to module

In order to be able to easily reuse the `$BIN` variable we created in
the test for the `clear` sub-command, move it to a Perl module that can
be included in other tests.

Add the `t/` directory to the include path when running `prove` to
ensure that `bin.pm` can be found and included.

Thanks to these resources for explaining Perl modules:
https://perlmaven.com/how-to-create-a-perl-module-for-code-reuse
https://stackoverflow.com/questions/23899121/perl-declare-and-export-variables-from-a-module/23900384#23900384
https://stackoverflow.com/questions/17931981/what-is-isa-in-perl/17932340#17932340

3 files changed, 15 insertions, 4 deletions

diff --git a/Makefile b/Makefile
index 2cab678..e67850b 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
 .PHONY: test
 
 test:
-	prove -v
+	prove -v -I./t
diff --git a/t/100-clear-clears-all-branches-from-list.t b/t/100-clear-clears-all-branches-from-list.t
index 952d68a..2e53350 100644
--- a/t/100-clear-clears-all-branches-from-list.t
+++ b/t/100-clear-clears-all-branches-from-list.t
@@ -4,9 +4,7 @@ use strict;
 
 use Test::More;
 
-use File::Spec;
-
-my $BIN = File::Spec->rel2abs('git-branch-list');
+use Bin qw($BIN);
 
 chdir 't-git-repo' or die $!;
 
diff --git a/t/bin.pm b/t/bin.pm
new file mode 100644
index 0000000..ad5b7f1
--- /dev/null
+++ b/t/bin.pm
@@ -0,0 +1,13 @@
+package Bin;
+
+use strict;
+use warnings;
+
+use Exporter qw(import);
+our @EXPORT = qw($BIN);
+
+use File::Spec;
+
+our $BIN = File::Spec->rel2abs('git-branch-list');
+
+1;