patch 8.0.0156: not enough test coverage for float functions

Problem:    Several float functions are not covered by tests.
Solution:   Add float tests. (Dominique Pelle)
diff --git a/src/testdir/test_alot.vim b/src/testdir/test_alot.vim
index d24b97f..6e989f6 100644
--- a/src/testdir/test_alot.vim
+++ b/src/testdir/test_alot.vim
@@ -16,6 +16,7 @@
 source test_fileformat.vim
 source test_filter_cmd.vim
 source test_filter_map.vim
+source test_float_func.vim
 source test_fnamemodify.vim
 source test_glob2regpat.vim
 source test_goto.vim