Make CsvsaExpectation a context manager

This gives us more context around assertion failures

Author: Owen Jones

regression/CSVSA/TestBasic/test_basic.py

@@ -6,10 +6,7 @@
 
 def test_tolerate_unreachable_functions():
     csvsa_driver = CsvsaDriver(folder_name).with_test_function('tolerate_unreachable_functions')
-    csvsa_expectation = csvsa_driver.run()
-
-    csvsa_expectation.check_successful_run()
-    csvsa_expectation.check_does_not_match("a \. f\(\)")
-    csvsa_expectation.check_does_not_match("a \. g\(\)")
-    csvsa_expectation.check_does_not_match("a \. f\(\)")
-    csvsa_expectation.check_does_not_match("a \. g\(\)")
+    with csvsa_driver.run() as csvsa_expectation:
+        csvsa_expectation.check_successful_run()
+        csvsa_expectation.check_does_not_match("a . f()")
+        csvsa_expectation.check_does_not_match("a . g()")

regression/CSVSA/csvsa_driver.py

@@ -4,12 +4,14 @@
 from regression.regex_expectation import RegexExpectation
 
 
+
 class CsvsaExpectation(RegexExpectation):
     """Encapsulate the output of CsvsaDriver"""
 
-    def __init__(self, goto_functions, return_code):
+    def __init__(self, goto_functions, return_code, cmdline):
         """Get the state at the end of test_function"""
-        RegexExpectation.__init__(self, goto_functions, return_code, compatibility_mode=False, check_verification=False)
+        RegexExpectation.__init__(self, goto_functions, return_code, compatibility_mode=False,
+                                  check_verification=False, cmdline=cmdline)
 
 
 class CsvsaDriver:
@@ -42,4 +44,4 @@ def run(self):
         executable_runner = ExecutableRunner(cmd)
         (stdout, _, return_code) = executable_runner.run(pipe_stderr_to_stdout=True)
 
-        return CsvsaExpectation(stdout, return_code)
+        return CsvsaExpectation(stdout, return_code, " ".join(cmd))

regression/regex_expectation.py

@@ -1,10 +1,11 @@
 import re
+import sys
 
 
 class RegexExpectation:
     """Encapsulate the output of CsvsaDriver"""
 
-    def __init__(self, text, return_code, compatibility_mode=True, check_verification=False):
+    def __init__(self, text, return_code, compatibility_mode=True, check_verification=False, cmdline=""):
         """Get the state at the end of test_function"""
         if return_code < 0:
             self.exit_code = 0
@@ -19,6 +20,7 @@ def __init__(self, text, return_code, compatibility_mode=True, check_verificatio
         self.split_text = text.splitlines()
         # check_verification indicates whether a successful run should include "VERIFICATION SUCCESSFUL" in it
         self.check_verification = check_verification
+        self.cmdline = cmdline
 
     def check_successful_run(self):
         self.check_does_not_match_regex("^warning: ignoring")
@@ -38,3 +40,10 @@ def check_matches_regex(self, x):
 
     def check_does_not_match_regex(self, x):
         assert all(not re.search(x, line) for line in self.split_text)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        if exc_value is not None:
+            print("Failure may relate to command: ", self.cmdline, file=sys.stderr)