Add possibility to test queries that are supposed to fail

This is supposed to be used for all malformed queries and all the ones
that are invalid for incompatibility reason, and make sure that they
actually fail.

driver.py

@@ -73,6 +73,9 @@ def execute_tests():
     ex_bad = 0
     ex_good = 0
     ex_tot = 0
+    f_tot = 0
+    f_good = 0
+    f_bad = 0
 
     for i in os.listdir(tests_path):
         if i.endswith('.query'):
@@ -93,6 +96,13 @@ def execute_tests():
                 ex_good += 1
             else:
                 ex_bad += 1
+        elif i.endswith('.fail'):
+            f_tot += 1
+            if run_fail_test(i[:-5]):
+                f_good += 1
+            else:
+                f_bad += 1
+
     print (colorize("Resume of the results", COLOR_CYAN))
 
     print (colorize("Query tests", COLOR_MAGENTA))
@@ -113,13 +123,19 @@ def execute_tests():
     if ex_bad > 0:
         print (colorize("Failed tests count: %d" % ex_bad, COLOR_RED))
 
+    print (colorize("Execute fail tests", COLOR_MAGENTA))
+    print ("Total test count: %d" % f_tot)
+    print ("Passed tests: %d" % f_good)
+    if f_bad > 0:
+        print (colorize("Failed tests count: %d" % f_bad, COLOR_RED))
+
     print (colorize("Total results", COLOR_CYAN))
-    if q_bad + py_bad + ex_bad == 0:
+    if f_bad + q_bad + py_bad + ex_bad == 0:
         print (colorize("No failed tests", COLOR_GREEN))
         return 0
     else:
         print (colorize("There are %d failed tests" %
-               (py_bad + q_bad + ex_bad), COLOR_RED))
+               (f_bad + py_bad + q_bad + ex_bad), COLOR_RED))
         return 1
 
 
@@ -170,6 +186,42 @@ def run_py_test(testname):
     print (colorize('=====================================', COLOR_RED))
     return False
 
+def run_fail_test(testname):
+    '''Runs a test, which executes a query that is supposed to fail'''
+    print ("Running fail test: " + colorize(testname, COLOR_MAGENTA))
+
+    query = readfile('%s%s.fail' % (tests_path, testname)).strip()
+    o_query = optimizer.optimize_all(query, rels)
+
+    expr = parser.parse(query)
+    o_expr = parser.parse(o_query)
+
+    test_succeed = True
+
+    try:
+        expr(rels)
+        test_succeed = False
+    except:
+        pass
+
+    try:
+        o_expr(rels)
+        test_succeed = False
+    except:
+        pass
+
+    c_expr = parser.tree(query).toCode()
+    try:
+        eval(c_expr, rels)
+        test_succeed = False
+    except:
+        pass
+
+    if test_succeed:
+        print (colorize('Test passed', COLOR_GREEN))
+    else:
+        print (colorize('Test failed (by not raising any exception)', COLOR_RED))
+    return test_succeed
 
 def run_test(testname):
     '''Runs a specific test executing the file