test(tests): run the UTF-8 suites on musl by falling back to C.UTF-8

.github/workflows/tests.yml

@@ -119,8 +119,8 @@ jobs:
       image: alpine:latest
 
     steps:
-      - name: Install bash, zsh and dash
-        run: apk add --no-cache bash zsh dash
+      - name: Install bash, zsh, dash and shellcheck
+        run: apk add --no-cache bash zsh dash shellcheck
 
       - name: Checkout code
         uses: actions/checkout@v7
@@ -137,7 +137,8 @@ jobs:
           adduser -D tester
           chown -R tester "$GITHUB_WORKSPACE"
           su tester -s /bin/sh -c 'cd tests && umask 022 &&
-            TEST_PARALLEL_JOBS=4 TEST_SHELLS="bash,bash --posix,zsh,dash,busybox sh" \
+            TEST_MAX_SKIPPED=10 TEST_PARALLEL_JOBS=4 \
+            TEST_SHELLS="bash,bash --posix,zsh,dash,busybox sh" \
             TEST_REQUIRE_SHELLS="zsh dash busybox" bash ./run_tests.sh'
 
   # Runs consumer-style scripts against the last release of the previous major version and

tests/run_tests.sh

@@ -594,6 +594,19 @@ main() {
     print_summary
     local exit_status=$?
 
+    # Optional skip-count guard (TEST_MAX_SKIPPED): when set, a run that skips more
+    # tests than the threshold fails, so a future environment change cannot silently
+    # reduce coverage again (Issue #152).
+    if [[ -n "${TEST_MAX_SKIPPED:-}" ]]; then
+        if ! [[ "$TEST_MAX_SKIPPED" =~ ^[0-9]+$ ]]; then
+            echo -e "${COLOR_RED}Error: TEST_MAX_SKIPPED must be a non-negative integer (got '$TEST_MAX_SKIPPED')${COLOR_RESET}"
+            exit_status=1
+        elif [[ "$SKIPPED_TESTS" -gt "$TEST_MAX_SKIPPED" ]]; then
+            echo -e "${COLOR_RED}Error: $SKIPPED_TESTS tests skipped, exceeding TEST_MAX_SKIPPED=$TEST_MAX_SKIPPED${COLOR_RESET}"
+            exit_status=1
+        fi
+    fi
+
     # Generate JUnit XML if requested
     if [[ "$JUNIT_OUTPUT" == "true" ]]; then
         generate_junit_xml "$OUTPUT_DIR/junit.xml"

tests/test_helpers.sh

@@ -203,6 +203,36 @@ skip_test() {
     teardown_test 0
 }
 
+# Return 0 when the system runs musl, where C.UTF-8 works without any installed locale
+# files (musl's default since 1.1.11, 2015). musl ships no `locale` utility, so
+# `locale -a` lists nothing even though C.UTF-8 (and every other locale name) is
+# available. Everything else, including glibc, returns 1 and keeps the `locale -a`
+# based detection.
+musl_c_utf8() {
+    command -v ldd >/dev/null 2>&1 || return 1
+    local ldd_banner
+    # musl's ldd prints the version banner (and exits nonzero) on stderr; glibc's prints on
+    # stdout. musl's ldd also exits 1, and run_tests.sh runs with pipefail, so the banner is
+    # captured first and the probe's status comes from grep alone.
+    ldd_banner="$(ldd --version 2>&1 || true)"
+    printf '%s\n' "$ldd_banner" | grep -qi musl
+}
+
+# Print an installed UTF-8 locale name, or nothing. On musl there is no `locale`
+# utility and no locale files, but C.UTF-8 still works (musl_c_utf8 above).
+utf8_locale_name() {
+    local candidate
+    for candidate in C.UTF-8 C.utf8 en_US.UTF-8 en_US.utf8; do
+        if locale -a 2>/dev/null | grep -qx "$candidate"; then
+            printf '%s\n' "$candidate"
+            return 0
+        fi
+    done
+    if musl_c_utf8; then
+        printf '%s\n' "C.UTF-8"
+    fi
+}
+
 # Assertion functions
 # shellcheck disable=SC2016
 

tests/test_posix_compat.sh

@@ -55,17 +55,6 @@ run_snippet_in_shell() {
     return "$status"
 }
 
-# Print an installed UTF-8 locale name, or nothing
-utf8_locale_name() {
-    local candidate
-    for candidate in C.UTF-8 C.utf8 en_US.UTF-8 en_US.utf8; do
-        if locale -a 2>/dev/null | grep -qx "$candidate"; then
-            printf '%s\n' "$candidate"
-            return 0
-        fi
-    done
-}
-
 test_posix_caller_detection() {
     local shell_command="$1"
     start_test "[$shell_command] script name is the calling script when sourced with ."
@@ -840,7 +829,11 @@ test_posix_levels_in_turkish_locale() {
     require_shell "${shell_command%% *}" || return 0
 
     if ! locale -a 2>/dev/null | grep -qiE '^tr_TR\.utf-?8$'; then
-        skip_test "tr_TR.UTF-8 locale not installed"
+        if musl_c_utf8; then
+            skip_test "musl has no locale-specific case mapping: the LC_ALL=C guard cannot be tested"
+        else
+            skip_test "tr_TR.UTF-8 locale not installed"
+        fi
         return 0
     fi
 

tests/test_shell_compat.sh

@@ -54,6 +54,13 @@ compat_locale_available() {
     if [[ "$normalized_wanted" == "c" || "$normalized_wanted" == "posix" ]]; then
         return 0
     fi
+    # The C.UTF-8 case goes through the shared helper (test_helpers.sh), which reports
+    # it on musl even though `locale -a` prints nothing there. Other names stay
+    # unavailable: musl only speaks UTF-8.
+    if [[ "$normalized_wanted" == "c.utf8" ]] \
+        && [[ "$(utf8_locale_name)" == "C.UTF-8" ]]; then
+        return 0
+    fi
     locale -a 2>/dev/null | tr '[:upper:]' '[:lower:]' | tr -d '-' \
         | grep -qx "$normalized_wanted"
 }

tests/test_validator_equivalence.sh

@@ -20,16 +20,11 @@ EQUIVALENCE_GOLDEN_DIR="$EQUIVALENCE_DIR/golden"
 EQUIVALENCE_DRIVER="$EQUIVALENCE_DIR/validator_driver.sh"
 
 # Print the name of an installed UTF-8 locale, or nothing.
-# The UTF-8 golden file records glibc's character classes, so it is only checked on Linux.
+# The UTF-8 golden file records glibc's character classes, so it is only checked on
+# Linux; the shared utf8_locale_name (test_helpers.sh) adds the musl C.UTF-8 fallback.
 equivalence_utf8_locale() {
     [[ "$(uname -s)" == "Linux" ]] || return 0
-    local candidate
-    for candidate in C.UTF-8 C.utf8 en_US.UTF-8 en_US.utf8; do
-        if locale -a 2>/dev/null | grep -qx "$candidate"; then
-            printf '%s\n' "$candidate"
-            return 0
-        fi
-    done
+    utf8_locale_name
 }
 
 # Print the check names used in a golden file, space separated