Ignore the squash! autosquash flag in subject

Because:

* `git-commit` uses a `squash!` prefix as a flag for autosquash with
  interactive rebase.
* The interactive rebase will strip the prefix, so the validation
  should ignore it when checking the subject for line length,
  capitalisation, etc.

This change:

* Strips the `squash!` prefix from the commit subject before
  validating.
* Adds tests for both the subject length and capitialisation
  validations with the `squash!` prefix.

Author: tommarshall

hook.sh

@@ -110,8 +110,8 @@ validate_commit_message() {
   # reset warnings
   WARNINGS=()
 
-  # capture the subject
-  COMMIT_SUBJECT=${COMMIT_MSG_LINES[0]}
+  # capture the subject, and remove the 'squash! ' prefix if present
+  COMMIT_SUBJECT=${COMMIT_MSG_LINES[0]/#squash! /}
 
   # if the commit is empty there's nothing to validate, we can return here
   COMMIT_MSG_STR="${COMMIT_MSG_LINES[*]}"

test/validation.bats

@@ -96,6 +96,14 @@ EOF
   assert_line --partial "Limit the subject line to 50 characters (51 chars)"
 }
 
+@test "validation: ignores squash! prefix when checking subject line length" {
+  echo "n" > $FAKE_TTY
+  run git commit -m "squash! Add foo bar string to my_file - As requested by Jo"
+
+  assert_success
+  refute_line --partial "Limit the subject line to 50 characters"
+}
+
 # 3. Capitalize the subject line
 # ------------------------------------------------------------------------------
 
@@ -131,6 +139,14 @@ EOF
   refute_line --partial "Capitalize the subject line"
 }
 
+@test "validation: ignores squash! prefix when checking subject line capitalisation" {
+  echo "n" > $FAKE_TTY
+  run git commit -m "squash! Add foo bar string to my_file"
+
+  assert_success
+  refute_line --partial "Capitalize the subject line"
+}
+
 # 4. Do not end the subject line with a period
 # ------------------------------------------------------------------------------