Added test cases for battery_percentage with pmset

Need to figure out way to ensure that pmset is used every time...

test/plugins/battery.plugin.bats

@@ -0,0 +1,36 @@
+#!/usr/bin/env bats
+
+load ../test_helper
+load ../../lib/composure
+
+cite _about _param _example _group _author _version
+
+load ../../lib/helpers
+load ../../plugins/available/battery.plugin
+
+@test 'plugins battery: battery-percentage with pmset, 100%' {
+  function pmset {
+    echo "-InternalBattery-0 (id=12345)	100%; discharging; 16:00 remaining present: true"
+  }
+
+  run battery_percentage
+  assert_output "100"
+}
+
+@test 'plugins battery: battery-percentage with pmset, 98%' {
+  function pmset {
+    echo "-InternalBattery-0 (id=12345)	98%; discharging; 16:00 remaining present: true"
+  }
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with pmset, 4%' {
+  function pmset {
+    echo "-InternalBattery-0 (id=12345)	4%; discharging; 16:00 remaining present: true"
+  }
+
+  run battery_percentage
+  assert_output "4"
+}