feat: add example of test plugin (for collection)

plugins/test_plugins/blue.py

@@ -0,0 +1,17 @@
+def is_blue(string):
+    blue_values = [
+        'blue',
+        '#0000ff',
+        '#00f',
+        'rgb(0,0,255)',
+        'rgb(0%,0%,100%)',
+    ]
+    if string in blue_values:
+        return True
+    else:
+        return False
+
+class TestModule(object):
+    ''' Ansible core blue test '''
+    def tests(self):
+        return {'blue': is_blue}