Refactor bash test build system a bit

The basic idea here is to separate a few intertwined notions:

1. Not all "run bash tests" are "install tests"

2. Not all "run bash tests" use `tests/functional/init.sh`, or any
   pre-test initialization at all.

This will used in the next commit when we have a test that check unit
test golden master data.

Also, move our custom `PS4` from the test to the test runner, as it is
part of how we want to display the tests, not the test themselves.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

mk/common-test.sh

@@ -1,15 +1,27 @@
-test_dir=tests/functional
+# Remove overall test dir (at most one of the two should match) and
+# remove file extension.
+test_name=$(echo -n "$test" | sed \
+    -e "s|^unit-test-data/||" \
+    -e "s|^tests/functional/||" \
+    -e "s|\.sh$||" \
+    )
 
-test=$(echo -n "$test" | sed -e "s|^$test_dir/||")
-
-TESTS_ENVIRONMENT=("TEST_NAME=${test%.*}" 'NIX_REMOTE=')
+TESTS_ENVIRONMENT=(
+    "TEST_NAME=$test_name"
+    'NIX_REMOTE='
+    'PS4=+(${BASH_SOURCE[0]-$0}:$LINENO) '
+)
 
 : ${BASH:=/usr/bin/env bash}
 
+run () {
+   cd "$(dirname $1)" && env "${TESTS_ENVIRONMENT[@]}" $BASH -x -e -u -o pipefail $(basename $1)
+}
+
 init_test () {
-   cd "$test_dir" && env "${TESTS_ENVIRONMENT[@]}" $BASH -e init.sh 2>/dev/null > /dev/null
+   run "$init" 2>/dev/null > /dev/null
 }
 
 run_test_proper () {
-   cd "$test_dir/$(dirname $test)" && env "${TESTS_ENVIRONMENT[@]}" $BASH -e $(basename $test)
+   run "$test"
 }