tests: expect_exit.py tool to replace "test $?"

tests/integration/lit.cfg

@@ -25,6 +25,8 @@ config.substitutions.append(('%FILECHECK_TESTER_EXEC', "{}/tests/integration/too
 cat_exec = "cat" if not is_windows() else "type"
 config.substitutions.append(('%cat', cat_exec))
 
+config.substitutions.append(('%expect_exit', 'python \"{}/tests/integration/tools/expect_exit.py\"'.format(current_dir)))
+
 if real_only:
     config.suffixes = ['.itest', '.itest-llvm', '.c']
 else:

tests/integration/tests/check_commands/CHECK-EMPTY/01-error_CHECK_EMPTY_without_previous_CHECK/sample.itest

@@ -1,4 +1,4 @@
-; RUN: cat %S/filecheck.input | (%FILECHECK_EXEC %S/filecheck.check 2>&1; test $? = 2) | %FILECHECK_TESTER_EXEC %s --match-full-lines
+; RUN: cat %S/filecheck.input | %expect_exit 2 %FILECHECK_EXEC "%S/filecheck.check" 2>&1 | %expect_exit 0 %FILECHECK_TESTER_EXEC "%s" --match-full-lines
 ; CHECK: {{^.*}}FileCheck{{(\.py)?$}}
 ; CHECK: {{.*}}filecheck.check:1:3: error: found 'CHECK-EMPTY' without previous 'CHECK: line{{$}}
 ; CHECK: {{^}}; CHECK-EMPTY:{{$}}

tests/integration/tools/expect_exit.py

@@ -0,0 +1,40 @@
+# import os
+import subprocess
+import sys
+
+if len(sys.argv) <= 2:
+    print("Expect arguments to be provided")
+    exit(1)
+
+expected_exit_code_arg = sys.argv[1]
+try:
+    expected_exit_code = int(expected_exit_code_arg)
+    if expected_exit_code < 0 or expected_exit_code > 127:
+        raise ValueError
+except ValueError:
+    print("expected numeric exit code within range [0, 127]: {}".format(expected_exit_code_arg))
+    exit(1)
+
+data = sys.stdin.readlines()
+
+args = sys.argv.copy()
+
+args.pop(0)
+args.pop(0)
+
+process = subprocess.Popen(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
+for line in data:
+    process.stdin.write(line.encode())
+
+output, error = process.communicate()
+
+output_lines = output.decode('utf-8').split('\n')
+del output_lines[-1]
+
+for word in output_lines:
+    print(word)
+
+if process.returncode == expected_exit_code:
+    exit(0)
+else:
+    exit(1)