Let Action fail if git binary can't be located (#261)

* Check if git binary exists

* Add Tests

action.yml

@@ -70,6 +70,9 @@ inputs:
   create_branch:
     description: Create new branch with the name of `branch`-input in local and remote repository, if it doesn't exist yet.
     default: false
+  internal_git_binary:
+    description: Internal use only! Path to git binary used to check if git is available. (Don't change this!)
+    default: git
 
 outputs:
   changes_detected:

entrypoint.sh

@@ -7,6 +7,8 @@ if "$INPUT_DISABLE_GLOBBING"; then
 fi
 
 _main() {
+    _check_if_git_is_available
+
     _switch_to_repository
 
     if _git_is_dirty || "$INPUT_SKIP_DIRTY_CHECK"; then
@@ -42,6 +44,14 @@ _main() {
     fi
 }
 
+_check_if_git_is_available() {
+    if hash -- "$INPUT_INTERNAL_GIT_BINARY" 2> /dev/null; then
+        echo "::debug::git binary found.";
+    else
+        echo "::error ::git-auto-commit could not find git binary. Please make sure git is available."
+        exit 1;
+    fi
+}
 
 _switch_to_repository() {
     echo "INPUT_REPOSITORY value: $INPUT_REPOSITORY";

tests/git-auto-commit.bats

@@ -37,6 +37,7 @@ setup() {
     export INPUT_SKIP_CHECKOUT=false
     export INPUT_DISABLE_GLOBBING=false
     export INPUT_CREATE_BRANCH=false
+    export INPUT_INTERNAL_GIT_BINARY=git
 
     # Set GitHub environment variables used by the GitHub Action
     temp_github_output_file=$(mktemp -t github_output_test.XXXXX)
@@ -1041,3 +1042,14 @@ cat_github_output() {
     assert_line "::set-output name=changes_detected::false"
     refute_line -e "::set-output name=commit_hash::[0-9a-f]{40}$"
 }
+
+@test "It fails hard if git is not available" {
+    INPUT_INTERNAL_GIT_BINARY=binary-does-not-exist
+
+    touch "${FAKE_LOCAL_REPOSITORY}"/new-file-{1,2,3}.txt
+
+    run git_auto_commit
+
+    assert_failure;
+    assert_line "::error ::git-auto-commit could not find git binary. Please make sure git is available."
+}