init: fix shell detection when invoked from a script

- fixes `ps` command to lookup parent process
 - adds `assert_output_contains_not` test helper

Ref: https://github.com/yyuu/pyenv/issues/373

test/init.bats

@@ -4,12 +4,29 @@ load test_helper
 
 @test "detect parent shell" {
   unset PYENV_SHELL
-  root="$(cd $BATS_TEST_DIRNAME/.. && pwd)"
   SHELL=/bin/false run pyenv-virtualenv-init -
   assert_success
   assert_output_contains '  PROMPT_COMMAND="_pyenv_virtualenv_hook;$PROMPT_COMMAND";'
 }
 
+@test "detect parent shell from script (sh)" {
+  unset PYENV_SHELL
+  printf '#!/bin/sh\necho "$(pyenv-virtualenv-init -)"' > ${BATS_TEST_DIRNAME}/script.sh
+  chmod +x ${BATS_TEST_DIRNAME}/script.sh
+  run ${BATS_TEST_DIRNAME}/script.sh
+  assert_success
+  assert_output_contains_not '  PROMPT_COMMAND="_pyenv_virtualenv_hook;$PROMPT_COMMAND";'
+}
+
+@test "detect parent shell from script (bash)" {
+  unset PYENV_SHELL
+  printf '#!/bin/bash\necho "$(pyenv-virtualenv-init -)"' > ${BATS_TEST_DIRNAME}/script.sh
+  chmod +x ${BATS_TEST_DIRNAME}/script.sh
+  run ${BATS_TEST_DIRNAME}/script.sh
+  assert_success
+  assert_output_contains '  PROMPT_COMMAND="_pyenv_virtualenv_hook;$PROMPT_COMMAND";'
+}
+
 @test "sh-compatible instructions" {
   run pyenv-virtualenv-init bash
   assert [ "$status" -eq 1 ]

test/test_helper.bash

@@ -97,6 +97,16 @@ assert_output_contains() {
   }
 }
 
+assert_output_contains_not() {
+  local expected="$1"
+  echo "$output" | grep -F "$expected" >/dev/null && {
+    { echo "expected output to not contain $expected"
+      echo "actual: $output"
+    } | flunk; return
+  }
+  return 0
+}
+
 create_executable() {
   mkdir -p "${PYENV_ROOT}/versions/$1/bin"
   touch "${PYENV_ROOT}/versions/$1/bin/$2"