fix(test-doubles): use builtin echo/printf in spy to prevent recursion when spying on echo or printf

Spying on 'echo' or 'printf' caused bashunit to hang indefinitely because
the generated spy function called back into itself through bashunit's
internal use of these builtins.

Changes:
- Use 'builtin echo' and 'builtin printf' inside the eval'd spy function
  body in bashunit::spy to prevent recursive calls when spying on echo
  or printf
- Use 'builtin echo' in bashunit::mock's no-arg form for the same reason
- Use 'builtin echo' in bashunit::helper::normalize_variable_name so that
  spy assertions remain functional even when echo is spied upon
- Add functional tests (with fixtures) verifying that spying on echo and
  printf completes without hanging

Fixes #607

Author: SauronBot

src/helpers.sh

@@ -261,7 +261,7 @@ function bashunit::helper::normalize_variable_name() {
     normalized_string="_$normalized_string"
   fi
 
-  echo "$normalized_string"
+  builtin echo "$normalized_string"
 }
 
 function bashunit::helper::get_provider_data() {

src/test_doubles.sh

@@ -34,7 +34,7 @@ function bashunit::mock() {
   if [[ $# -gt 0 ]]; then
     eval "function $command() { $* \"\$@\"; }"
   else
-    eval "function $command() { echo \"$($CAT)\" ; }"
+    eval "function $command() { builtin echo \"$($CAT)\" ; }"
   fi
 
   export -f "${command?}"
@@ -61,14 +61,14 @@ function bashunit::spy() {
     local serialized=\"\"
     local arg
     for arg in \"\$@\"; do
-      serialized=\"\$serialized\$(printf '%q' \"\$arg\")$'\\x1f'\"
+      serialized=\"\$serialized\$(builtin printf '%q' \"\$arg\")$'\\x1f'\"
     done
     serialized=\${serialized%$'\\x1f'}
-    printf '%s\x1e%s\\n' \"\$raw\" \"\$serialized\" >> '$params_file'
+    builtin printf '%s\x1e%s\\n' \"\$raw\" \"\$serialized\" >> '$params_file'
     local _c
-    _c=\$(cat '$times_file' 2>/dev/null || echo 0)
+    _c=\$(cat '$times_file' 2>/dev/null || builtin echo 0)
     _c=\$((_c+1))
-    echo \"\$_c\" > '$times_file'
+    builtin echo \"\$_c\" > '$times_file'
   }"
 
   export -f "${command?}"

tests/functional/doubles_test.sh

@@ -89,3 +89,21 @@ function test_spy_commands_called_once_when_executing_a_sourced_function() {
   assert_have_been_called_times 1 awk
   assert_have_been_called_times 1 head
 }
+
+function test_spy_on_echo_does_not_hang() {
+  source ./tests/functional/fixtures/echo_function.sh
+  bashunit::spy echo
+
+  write_message "hello world"
+
+  assert_have_been_called echo
+}
+
+function test_spy_on_printf_does_not_hang() {
+  source ./tests/functional/fixtures/printf_function.sh
+  bashunit::spy printf
+
+  format_message "hello world"
+
+  assert_have_been_called printf
+}

tests/functional/fixtures/echo_function.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+function write_message() {
+  echo "message: $*"
+}

tests/functional/fixtures/printf_function.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+function format_message() {
+  printf "formatted: %s\n" "$*"
+}

tests/unit/test_doubles_test.sh

@@ -214,3 +214,5 @@ function test_unsuccessful_spy_nth_called_with_invalid_index() {
       "expected call" "at index 5 but" "only called 1 times")" \
     "$(assert_have_been_called_nth_with 5 ps "first")"
 }
+
+