[Tests] run every remaining test file: exec bits, fixes; add check-exec to CI

urchin only executes test files that have the executable bit, silently skipping the rest,
and `npm run test:check-exec` would catch non-executable ones, but no workflow ran it -
so several test files have never actually run.
Make all of them executable, and fix the ones that were broken:
- the io.js source-install tests, skipped since 2016: io.js requires python 2 and gcc <= 5,
so they now skip on toolchains that can not compile it,
and a new gcc:4.9-container CI job runs them unmodified -
resolving, downloading, checksumming, and compiling io.js for real.
New `fake source` variants exercise nvm's source pipeline everywhere -
cache lookup, offline resolution, extraction, configure, make, make install, activation -
via a tiny fake source tree seeded into the download cache and installed with `--offline`.
Also strengthen the `nvm run | grep` assertions with `--silent`,
since the version banner used to satisfy the grep even when the built binary could not run,
and give the final assertions the `die` they always meant to call.
- `nvm uninstall ... incorrect file permissions fails nicely`, parked in 2025 as failing:
`sudo npm` resets PATH, so node 5's npm crashed under the system node.
The permissions check only trips on files that are neither writable nor self-owned,
and that precondition only needs `sudo touch` - not npm, jspm, or the network -
so use that, against a fake installed version,
and skip only where passwordless sudo does not exist.
- `nvm install --offline`: `nvm ls | tail -1` always grabbed an alias line, never a version;
use `nvm_ls` and skip its trailing `system <version>` line.
- `nvm exec ... help should not parse`: in a BRE, `[options]` is a bracket expression,
so the grep could never match node's literal `Usage: node [options]` output.
- `nvm use ... nvmrc containing not installed version`: current output once again matches its expectations verbatim; no changes needed.

Rewrite `test:check-exec` in POSIX sh - npm runs scripts with /bin/sh, which is dash on Ubuntu,
where the previous `[[`/`$'\n'` bashisms would break;
match by extension, so that filenames containing dots can not dodge the check;
and disable git's `core.quotePath` mangling of the non-ASCII test filenames.
Then wire it into the lint workflow.

test/slow/nvm exec/Running 'nvm exec' with help should not parse

@@ -6,4 +6,6 @@ die () { echo "$@" ; exit 1; }
 
 nvm use 0.10
 
-nvm exec stable -- node --help | grep 'Usage: node [options]' || die "Help menu should have been displayed for node and not nvm"
+# note: in a BRE, `[options]` is a bracket expression, so the literal `[options]`
+# in node's help output could never match; match the unbracketed prefix instead
+nvm exec stable -- node --help | grep 'Usage: node' || die "Help menu should have been displayed for node and not nvm"

test/slow/nvm uninstall/Running 'nvm uninstall' with incorrect file permissions fails nicely

@@ -1,30 +1,51 @@
 #!/bin/sh
 
-die () { echo "$@" ; exit 1; }
+die () { echo "$@" ; cleanup ; exit 1; }
 
 # Source nvm
 \. ../../../nvm.sh
 
-# Version to install/uninstall
-NVM_TEST_VERSION=5.10.1
+\. ../../common.sh
 
-# Make sure it's not already here
-[ -e ../../../$NVM_TEST_VERSION ] && rm -R ../../../$NVM_TEST_VERSION
+NVM_TEST_VERSION=v5.99.99
 
-# Install it
-nvm install $NVM_TEST_VERSION
+cleanup() {
+  VERSION_PATH="${VERSION_PATH-}"
+  if [ -n "${VERSION_PATH}" ] && [ -d "${VERSION_PATH}" ]; then
+    sudo -n rm -f "${VERSION_PATH}/lib/root-owned-file" 2>/dev/null
+    rm -rf "${VERSION_PATH}"
+  fi
+}
 
-# Make sure it installed
-nvm ls | grep "$NVM_TEST_VERSION" || die "Failed to install node"
+# The permissions check only trips on files that are neither writable nor
+# self-owned, and creating one requires another user: skip where passwordless
+# sudo is unavailable; CI always has it.
+if ! sudo -n true 2>/dev/null; then
+  echo 'passwordless sudo is not available, skipping'
+  exit 0
+fi
 
-# Install global module as root
-npm_path=$(which npm)
-sudo -n "$npm_path" install jspm@'<2' -g || die 'either sudo failed, or `npm install jspm -g` failed`'
+# Install a fake version to uninstall
+make_fake_node "${NVM_TEST_VERSION}" || die 'unable to make fake node'
+VERSION_PATH="$(nvm_version_path "${NVM_TEST_VERSION}")"
 
-# Switch to another version so we can uninstall
-nvm use 0.12.7
+# Make part of the installation folder unwritable, and not self-owned
+mkdir -p "${VERSION_PATH}/lib"
+sudo -n touch "${VERSION_PATH}/lib/root-owned-file" || die 'sudo touch failed'
+sudo -n chmod 444 "${VERSION_PATH}/lib/root-owned-file" || die 'sudo chmod failed'
+
+# Make sure the version to uninstall is not the active one
+nvm deactivate >/dev/null 2>&1 || true
 
 # Attempt to uninstall it
-RETURN_MESSAGE="$(nvm uninstall $NVM_TEST_VERSION 2>&1)"
+RETURN_MESSAGE="$(nvm uninstall "${NVM_TEST_VERSION}" 2>&1)"
 CHECK_FOR="Cannot uninstall, incorrect permissions on installation folder"
-test "${RETURN_MESSAGE#*$CHECK_FOR}" != "$RETURN_MESSAGE" || die "Failed to show error message"
+case "${RETURN_MESSAGE}" in
+  *"${CHECK_FOR}"*) ;;
+  *) die "Failed to show error message; got: ${RETURN_MESSAGE}" ;;
+esac
+
+# ... and the version must not have been removed
+nvm_is_version_installed "${NVM_TEST_VERSION}" || die 'version was uninstalled despite the permissions error'
+
+cleanup