test: Drop the blank line before test macros

Most tests don't have this. It helps to keep the test declaration
clearly associated with the function it relates to, rather than the next
one in the file. Remove the extra blank line and mention this in the
docs.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/tests_writing.rst b/doc/develop/tests_writing.rst
index 655eb95..c277c8d 100644
--- a/doc/develop/tests_writing.rst
+++ b/doc/develop/tests_writing.rst
@@ -228,6 +228,9 @@
    }
    DM_TEST(dm_test_uclassname_what, UTF_SCAN_FDT);
 
+Note that the convention is to NOT add a blank line before the macro, so that
+the function it relates to is more obvious.
+
 Replace 'uclassname' with the name of your uclass, if applicable. Replace 'what'
 with what you are testing.