kunit: Add speed attribute

Add speed attribute to the test attribute API. This attribute will allow
users to mark tests with a category of speed.

Currently the categories of speed proposed are: normal, slow, and very_slow
(outlined in enum kunit_speed). These are outlined in the enum kunit_speed.

The assumed default speed for tests is "normal". This indicates that the
test takes a relatively trivial amount of time (less than 1 second),
regardless of the machine it is running on. Any test slower than this could
be marked as "slow" or "very_slow".

Add the macro KUNIT_CASE_SLOW to set a test as slow, as this is likely a
common use of the attributes API.

Add an example of marking a slow test to kunit-example-test.c.

Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Rae Moar <rmoar@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

include/kunit/test.h

@@ -63,8 +63,27 @@ enum kunit_status {
 	KUNIT_SKIPPED,
 };
 
+/* Attribute struct/enum definitions */
+
+/*
+ * Speed Attribute is stored as an enum and separated into categories of
+ * speed: very_slowm, slow, and normal. These speeds are relative to
+ * other KUnit tests.
+ *
+ * Note: unset speed attribute acts as default of KUNIT_SPEED_NORMAL.
+ */
+enum kunit_speed {
+	KUNIT_SPEED_UNSET,
+	KUNIT_SPEED_VERY_SLOW,
+	KUNIT_SPEED_SLOW,
+	KUNIT_SPEED_NORMAL,
+	KUNIT_SPEED_MAX = KUNIT_SPEED_NORMAL,
+};
+
 /* Holds attributes for each test case and suite */
-struct kunit_attributes {};
+struct kunit_attributes {
+	enum kunit_speed speed;
+};
 
 /**
  * struct kunit_case - represents an individual test case.
@@ -150,6 +169,17 @@ static inline char *kunit_status_to_ok_not_ok(enum kunit_status status)
 		{ .run_case = test_name, .name = #test_name,	\
 		  .attr = attributes }
 
+/**
+ * KUNIT_CASE_SLOW - A helper for creating a &struct kunit_case
+ * with the slow attribute
+ *
+ * @test_name: a reference to a test case function.
+ */
+
+#define KUNIT_CASE_SLOW(test_name)			\
+		{ .run_case = test_name, .name = #test_name,	\
+		  .attr.speed = KUNIT_SPEED_SLOW }
+
 /**
  * KUNIT_CASE_PARAM - A helper for creation a parameterized &struct kunit_case
  *