Fix imperative mood false positives

Because:

* The imperative mood check is incorrectly reporting a warning when a
  commit subject is in imperative mood, but contains a word on the
  blacklist, e.g. "Remove the temporary fixes to foo"
* This is because the check is currently checking for the presence of
  the blacklist words anywhere in the string.

This change:

* Add test for the false positive case.
* Fix the issue by having the check test only the first word of the
  subject against the blacklist.

Notes:

* This may lead to some false negatives, but it's best effort, and the
  false positives are coming up relatively frequently.

Author: tommarshall

hook.sh

@@ -180,7 +180,7 @@ validate_commit_message() {
   shopt -s nocasematch
 
   for BLACKLISTED_WORD in "${IMPERATIVE_MOOD_BLACKLIST[@]}"; do
-    [[ ${COMMIT_SUBJECT} =~ $BLACKLISTED_WORD ]]
+    [[ ${COMMIT_SUBJECT} =~ ^[[:blank:]]*$BLACKLISTED_WORD ]]
     test $? -eq 0 && add_warning 1 "Use the imperative mood in the subject line, e.g 'fix' not 'fixes'" && break
   done
 

test/validation.bats

@@ -172,30 +172,38 @@ EOF
 # 5. Use the imperative mood in the subject line
 # ------------------------------------------------------------------------------
 
-@test "validation: subject line with 'fixes' shows warning" {
+@test "validation: subject line starting with 'fixes' shows warning" {
   echo "n" > $FAKE_TTY
-  run git commit -m "More fixes for broken stuff"
+  run git commit -m "Fixes for broken stuff"
 
   assert_failure
   assert_line --partial "Use the imperative mood in the subject line"
 }
 
-@test "validation: subject line with 'fixed' shows warning" {
+@test "validation: subject line starting with 'fixed' shows warning" {
   echo "n" > $FAKE_TTY
   run git commit -m "Fixed bug with Y"
 
   assert_failure
   assert_line --partial "Use the imperative mood in the subject line"
 }
 
-@test "validation: subject line with 'fixing' shows warning" {
+@test "validation: subject line starting with 'fixing' shows warning" {
   echo "n" > $FAKE_TTY
   run git commit -m "Fixing behavior of X"
 
   assert_failure
   assert_line --partial "Use the imperative mood in the subject line"
 }
 
+@test "validation: subject line in imperative mood with 'fixes' does not show warning" {
+  echo "n" > $FAKE_TTY
+  run git commit -m "Remove the temporary fixes to Y"
+
+  assert_success
+  refute_line --partial "Use the imperative mood in the subject line"
+}
+
 @test "validation: body with 'fixes', 'fixed', 'fixing' does not show warning" {
   run git commit -m "$(cat <<EOF
 Add foo bar string to my_file