Suppress certain stderr-printing during tests

Tests that exercise error paths may result in output to
stderr. This may make it look like the test failed when it did
not. Introduce should_suppress_stderr_for_tests() to suppress
this output so the test output looks clean.

src/builtin_test.cpp

@@ -820,7 +820,7 @@ int builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
 
     wcstring_list_t eval_errors;
     bool result = expr->evaluate(eval_errors);
-    if (!eval_errors.empty()) {
+    if (!eval_errors.empty() && ! should_suppress_stderr_for_tests()) {
         printf("test returned eval errors:\n");
         for (size_t i = 0; i < eval_errors.size(); i++) {
             printf("\t%ls\n", eval_errors.at(i).c_str());

src/common.cpp

@@ -533,11 +533,15 @@ ssize_t read_loop(int fd, void *buff, size_t count) {
     return result;
 }
 
+bool should_suppress_stderr_for_tests() {
+    // Hack to not print error messages in the tests.
+    return program_name && !wcscmp(program_name, TESTS_PROGRAM_NAME);
+}
+
 static bool should_debug(int level) {
     if (level > debug_level) return false;
 
-    // Hack to not print error messages in the tests.
-    if (program_name && !wcscmp(program_name, L"(ignore)")) return false;
+    if (should_suppress_stderr_for_tests()) return false;
 
     return true;
 }

src/common.h

@@ -373,6 +373,10 @@ string_fuzzy_match_t string_fuzzy_match_string(const wcstring &string,
 /// Test if a list contains a string using a linear search.
 bool list_contains_string(const wcstring_list_t &list, const wcstring &str);
 
+// Check if we are running in the test mode, where we should suppress error output
+#define TESTS_PROGRAM_NAME L"(ignore)"
+bool should_suppress_stderr_for_tests();
+
 void assert_is_main_thread(const char *who);
 #define ASSERT_IS_MAIN_THREAD_TRAMPOLINE(x) assert_is_main_thread(x)
 #define ASSERT_IS_MAIN_THREAD() ASSERT_IS_MAIN_THREAD_TRAMPOLINE(__FUNCTION__)

src/fish_tests.cpp

@@ -4072,7 +4072,9 @@ int main(int argc, char **argv) {
     srand((unsigned int)time(NULL));
     configure_thread_assertions_for_testing();
 
-    program_name = L"(ignore)";
+    // Set the program name to this sentinel value
+    // This will prevent some misleading stderr output during the tests
+    program_name = TESTS_PROGRAM_NAME;
     s_arguments = argv + 1;
 
     struct utsname uname_info;

src/parse_execution.cpp

@@ -708,7 +708,8 @@ parse_execution_result_t parse_execution_context_t::report_errors(
         parser->get_backtrace(src, error_list, &backtrace_and_desc);
 
         // Print it.
-        fprintf(stderr, "%ls", backtrace_and_desc.c_str());
+        if (! should_suppress_stderr_for_tests())
+            fprintf(stderr, "%ls", backtrace_and_desc.c_str());
     }
     return parse_execution_errored;
 }