fix(coverage): printf spy no longer breaks coverage collection

CHANGELOG.md

@@ -8,6 +8,7 @@
 ### Fixed
 - A test that exited non-zero no longer poisons the exit code of subsequent tests in the same file (the per-test exit code was accumulated instead of reset)
 - Coverage report now counts backslash line-continuation lines as covered: a multi-line statement's hit is propagated forward across its continuation chain, so the lines after a trailing `\` are no longer reported as uncovered (#722)
+- Spying or mocking the `printf` builtin no longer breaks coverage collection: the coverage buffer is now flushed with `builtin printf`, so a test double can no longer shadow the write and silently drop all coverage data for that test (#724)
 
 ### Changed
 - Documentation and project URLs now point to the new primary domain `bashunit.com` (old `bashunit.typeddevs.com` continues to work as a redirect)

src/coverage.sh

@@ -330,11 +330,13 @@ function bashunit::coverage::flush_buffer() {
     test_hits_file="${_BASHUNIT_COVERAGE_TEST_HITS_FILE}.$$"
   fi
 
-  # Write buffered data in a single I/O operation
-  printf '%s' "$_BASHUNIT_COVERAGE_BUFFER" >>"$data_file"
+  # Write buffered data in a single I/O operation.
+  # Use `builtin printf` so a user test spying/mocking the printf builtin
+  # cannot shadow the coverage write and silently drop data (see issue #724).
+  builtin printf '%s' "$_BASHUNIT_COVERAGE_BUFFER" >>"$data_file"
 
   if [ -n "$_BASHUNIT_COVERAGE_HITS_BUFFER" ]; then
-    printf '%s' "$_BASHUNIT_COVERAGE_HITS_BUFFER" >>"$test_hits_file"
+    builtin printf '%s' "$_BASHUNIT_COVERAGE_HITS_BUFFER" >>"$test_hits_file"
   fi
 
   # Reset buffer

tests/unit/coverage_core_test.sh

@@ -268,6 +268,33 @@ function test_coverage_record_line_writes_to_file() {
   assert_contains "$test_file:20" "$content"
 }
 
+function test_coverage_flush_buffer_writes_even_when_printf_is_spied() {
+  BASHUNIT_COVERAGE="true"
+  BASHUNIT_COVERAGE_PATHS="/"
+  BASHUNIT_COVERAGE_EXCLUDE=""
+  bashunit::coverage::init
+
+  local test_file="/some/path/script.sh"
+  bashunit::coverage::record_line "$test_file" "10"
+  bashunit::coverage::record_line "$test_file" "20"
+
+  # Spying printf must not shadow the coverage write (issue #724)
+  bashunit::spy printf
+  bashunit::coverage::flush_buffer
+  bashunit::unmock printf
+
+  local data_file="$_BASHUNIT_COVERAGE_DATA_FILE"
+  if bashunit::parallel::is_enabled; then
+    data_file="${_BASHUNIT_COVERAGE_DATA_FILE}.$$"
+  fi
+
+  local content
+  content=$(cat "$data_file")
+
+  assert_contains "$test_file:10" "$content"
+  assert_contains "$test_file:20" "$content"
+}
+
 function test_coverage_cleanup_removes_temp_files() {
   BASHUNIT_COVERAGE="true"
   bashunit::coverage::init