avocado.main(): avoid an infinite fork loop bomb

Because the current implementation of avocado.main() creates a job
and runs "sys.argv[0]" to implement standalone mode, it ends up
running itself over and over.

This simple proposed fix, prevents avocado.main() from running
itself again if called from itself. Since they are on different
processes, the mechanism chosen to do this is to set an environment
variable, that will be seen by the next process.

Also, by exiting from main() with an error code, the test first
level test will fail. This will let the user know that the chosen
approach (SIMPLE tests written in Python and calling main()) are
not worthy of a PASS.

This adresses issue avocado-framework#961.

Signed-off-by: Cleber Rosa <crosa@redhat.com>

avocado/core/job.py

@@ -540,6 +540,16 @@ class TestProgram(object):
     """
 
     def __init__(self):
+        # Avoid fork loop/bomb when running a test via avocado.main() that
+        # calls avocado.main() itself
+        if os.environ.get('AVOCADO_STANDALONE_IN_MAIN', False):
+            sys.stderr.write('AVOCADO_STANDALONE_IN_MAIN environment variable '
+                             'found. This means that this code is being '
+                             'called recursively. Exiting to avoid an infinite'
+                             ' fork loop.\n')
+            sys.exit(exit_codes.AVOCADO_FAIL)
+        os.environ['AVOCADO_STANDALONE_IN_MAIN'] = 'True'
+
         self.defaultTest = sys.argv[0]
         self.progName = os.path.basename(sys.argv[0])
         self.parseArgs(sys.argv[1:])

selftests/functional/test_loader.py

@@ -82,7 +82,6 @@ def test(self):
     main()
 """
 
-
 NOT_A_TEST = """
 def hello():
     print('Hello World!')
@@ -100,6 +99,40 @@ def hello():
 true
 """
 
+AVOCADO_SIMPLE_PYTHON_LIKE_MULTIPLE_FILES = """#!/usr/bin/env python
+# A simple test (executable bit set when saved to file) that looks like
+# an Avocado instrumented test, with base class on separate file
+from avocado import Test
+from avocado import main
+from test2 import *
+
+class BasicTestSuite(SuperTest):
+
+    def test1(self):
+        self.xxx()
+        self.assertTrue(True)
+
+if __name__ == '__main__':
+    main()
+"""
+
+AVOCADO_SIMPLE_PYTHON_LIKE_MULTIPLE_FILES_LIB = """
+#!/usr/bin/python
+
+from avocado import Test
+
+class SuperTest(Test):
+    def xxx(self):
+        print "ahoj"
+"""
+
+AVOCADO_TEST_SIMPLE_USING_MAIN = """#!/usr/bin/env python
+from avocado import main
+
+if __name__ == "__main__":
+    main()
+"""
+
 
 class LoaderTestFunctional(unittest.TestCase):
 
@@ -161,6 +194,39 @@ def test_load_not_a_test(self):
     def test_load_not_a_test_not_exec(self):
         self._test('notatest.py', NOT_A_TEST, 'NOT_A_TEST')
 
+    def test_runner_simple_python_like_multiple_files(self):
+        mylib = script.TemporaryScript(
+            'test2.py',
+            AVOCADO_SIMPLE_PYTHON_LIKE_MULTIPLE_FILES_LIB,
+            'avocado_simpletest_functional',
+            0644)
+        mylib.save()
+        mytest = script.Script(
+            os.path.join(os.path.dirname(mylib.path), 'test.py'),
+            AVOCADO_SIMPLE_PYTHON_LIKE_MULTIPLE_FILES)
+        os.chdir(basedir)
+        mytest.save()
+        cmd_line = "./scripts/avocado list -V %s" % mytest
+        result = process.run(cmd_line)
+        self.assertIn('SIMPLE: 1', result.stdout)
+        # job should be able to finish under 5 seconds. If this fails, it's
+        # possible that we hit the "simple test fork bomb" bug
+        cmd_line = ("./scripts/avocado run --sysinfo=off --job-results-dir %s "
+                    "--job-timeout=5s %s" % (self.tmpdir, mytest))
+        process.run(cmd_line)
+
+    def test_simple_using_main(self):
+        mytest = script.TemporaryScript("simple_using_main.py",
+                                        AVOCADO_TEST_SIMPLE_USING_MAIN,
+                                        'avocado_simpletest_functional')
+        mytest.save()
+        os.chdir(basedir)
+        # job should be able to finish under 5 seconds. If this fails, it's
+        # possible that we hit the "simple test fork bomb" bug
+        cmd_line = ("./scripts/avocado run --sysinfo=off --job-results-dir %s "
+                    "--job-timeout=5s %s" % (self.tmpdir, mytest))
+        process.run(cmd_line)
+
     def tearDown(self):
         shutil.rmtree(self.tmpdir)