fix: reimplement load to be more useable and consistent

Existing support is preserved (absolute paths and relative paths with a `.bash` suffix), and now *any* relative path is supported, as well as scripts on the system `PATH`.

Fixes sstephenson#79

lib/bats-core/test_functions.bash

@@ -3,24 +3,30 @@
 BATS_TEST_DIRNAME="${BATS_TEST_FILENAME%/*}"
 BATS_TEST_NAMES=()
 
+# Shorthand for source-ing files relative to the BATS_TEST_DIRNAME,
+# optionally with a .bash suffix appended. If the argument doesn't
+# resolve relative to BATS_TEST_DIRNAME it is sourced as-is.
 load() {
-  local name="$1"
-  local filename
+  local file="${1:?}"
 
-  if [[ "${name:0:1}" == '/' ]]; then
-    filename="${name}"
-  else
-    filename="$BATS_TEST_DIRNAME/${name}.bash"
+  # For backwards-compatibility first look for a .bash-suffixed file.
+  # TODO consider flipping the order here; it would be more consistent
+  # and less surprising to look for an exact-match first.
+  if [[ -f "${BATS_TEST_DIRNAME}/${file}.bash" ]]; then
+    file="${BATS_TEST_DIRNAME}/${file}.bash"
+  elif [[ -f "${BATS_TEST_DIRNAME}/${file}" ]]; then
+    file="${BATS_TEST_DIRNAME}/${file}"
   fi
 
-  if [[ ! -f "$filename" ]]; then
-    printf 'bats: %s does not exist\n' "$filename" >&2
+  if [[ ! -f "$file" ]] && ! type -P "$file" >/dev/null; then
+    printf 'bats: %s does not exist\n' "$file" >&2
     exit 1
   fi
 
-  # Dynamically loaded user files provided outside of Bats.
+  # Dynamically loaded user file provided outside of Bats.
+  # Note: 'source "$file" || exit' doesn't work on bash3.2.
   # shellcheck disable=SC1090
-  source "${filename}"
+  source "${file}"
 }
 
 run() {

test/bats.bats

@@ -196,6 +196,11 @@ fixtures bats
   [ $status -eq 0 ]
 }
 
+@test "load sources relative scripts with filename extension" {
+  HELPER_NAME="test_helper.bash" run bats "$FIXTURE_ROOT/load.bats"
+  [ $status -eq 0 ]
+}
+
 @test "load aborts if the specified script does not exist" {
   HELPER_NAME="nonexistent" run bats "$FIXTURE_ROOT/load.bats"
   [ $status -eq 1 ]
@@ -211,6 +216,19 @@ fixtures bats
   [ $status -eq 1 ]
 }
 
+@test "load relative script with ambiguous name" {
+  HELPER_NAME="ambiguous" run bats "$FIXTURE_ROOT/load.bats"
+  [ $status -eq 0 ]
+}
+
+@test "load supports scripts on the PATH" {
+  path_dir="$BATS_TMPNAME/path"
+  mkdir -p "$path_dir"
+  cp "${FIXTURE_ROOT}/test_helper.bash" "${path_dir}/on_path"
+  PATH="${path_dir}:$PATH"  HELPER_NAME="on_path" run bats "$FIXTURE_ROOT/load.bats"
+  [ $status -eq 0 ]
+}
+
 @test "output is discarded for passing tests and printed for failing tests" {
   run bats "$FIXTURE_ROOT/output.bats"
   [ $status -eq 1 ]

test/fixtures/bats/ambiguous

@@ -0,0 +1,5 @@
+# Helper to detect regressions in load's lookup ordering.
+# An exact name match should be prioritized over name.bash.
+
+echo "Should not have loaded this file!" >&2
+exit 1

test/fixtures/bats/ambiguous.bash

@@ -0,0 +1,6 @@
+# Helper to detect regressions in load's lookup ordering.
+# An exact name match should be prioritized over name.bash.
+
+echo "This is the expected file to load."
+
+help_me() { :; }