Merge branch 'ab/test-must-be-empty-for-master'

Test updates.

* ab/test-must-be-empty-for-master:
tests: make use of the test_must_be_empty function

diff --cc t/t1507-rev-parse-upstream.sh
Simple merge

diff --cc t/t2202-add-addremove.sh
Simple merge

diff --cc t/t3700-add.sh
Simple merge

diff --cc t/t4010-diff-pathspec.sh
Simple merge

diff --cc t/t4015-diff-whitespace.sh
Simple merge

diff --cc t/t4202-log.sh
Simple merge

diff --cc t/t5505-remote.sh
Simple merge

diff --cc t/t5512-ls-remote.sh
Simple merge

diff --cc t/t7004-tag.sh
Simple merge

diff --cc t/t7030-verify-tag.sh
Simple merge

diff --cc t/t7063-status-untracked-cache.sh
Simple merge

diff --cc t/t7610-mergetool.sh
Simple merge

diff --cc t/t7810-grep.sh
Simple merge

diff --cc t/t9001-send-email.sh
Simple merge

diff --cc t/t9300-fast-import.sh
Simple merge