make test: improve robustness and performance

Introduce an API which asserts empty capture for interface.
Throw exception in old API if the capture does not exist, thus
making it clear if the test expects packets to arrive or not.
Improve performance by not doing sleeps after starting the packet
generator, rather lazily deleting captures when needed.
Fix wrong usage of packet.show() in various tests.

Change-Id: I456cb23316eef99b3f35f80344fe595c4db9a21c
Signed-off-by: Klement Sekera <ksekera@cisco.com>

test/vpp_pg_interface.py

@@ -6,7 +6,7 @@ from vpp_interface import VppInterface
 from scapy.layers.l2 import Ether, ARP
 from scapy.layers.inet6 import IPv6, ICMPv6ND_NS, ICMPv6ND_NA,\
     ICMPv6NDOptSrcLLAddr, ICMPv6NDOptDstLLAddr
-from util import ppp
+from util import ppp, ppc
 
 
 class VppPGInterface(VppInterface):
@@ -114,25 +114,71 @@ class VppPGInterface(VppInterface):
         except:
             pass
         wrpcap(self.in_path, pkts)
+        self.test.register_capture(self.cap_name)
         # FIXME this should be an API, but no such exists atm
         self.test.vapi.cli(self.input_cli)
-        self.test.pg_streams.append(self.cap_name)
-        self.test.vapi.cli("trace add pg-input %d" % len(pkts))
 
-    def get_capture(self):
+    def get_capture(self, remark=None):
         """
         Get captured packets
 
         :returns: iterable packets
         """
         try:
+            self.wait_for_capture_file()
             output = rdpcap(self.out_path)
         except IOError:  # TODO
-            self.test.logger.error("File %s does not exist, probably because no"
+            self.test.logger.debug("File %s does not exist, probably because no"
                                    " packets arrived" % self.out_path)
-            return []
+            if remark:
+                raise Exception("No packets captured on %s(%s)" %
+                                (self.name, remark))
+            else:
+                raise Exception("No packets captured on %s" % self.name)
         return output
 
+    def assert_nothing_captured(self, remark=None):
+        if os.path.isfile(self.out_path):
+            try:
+                capture = self.get_capture()
+                self.test.logger.error(
+                    ppc("Unexpected packets captured:", capture))
+            except:
+                pass
+            if remark:
+                raise AssertionError(
+                    "Capture file present for interface %s(%s)" %
+                    (self.name, remark))
+            else:
+                raise AssertionError("Capture file present for interface %s" %
+                                     self.name)
+
+    def wait_for_capture_file(self, timeout=1):
+        """
+        Wait until pcap capture file appears
+
+        :param timeout: How long to wait for the packet (default 1s)
+
+        :raises Exception: if the capture file does not appear within timeout
+        """
+        limit = time.time() + timeout
+        if not os.path.isfile(self.out_path):
+            self.test.logger.debug(
+                "Waiting for capture file to appear, timeout is %ss", timeout)
+        else:
+            self.test.logger.debug("Capture file already exists")
+            return
+        while time.time() < limit:
+            if os.path.isfile(self.out_path):
+                break
+            time.sleep(0)  # yield
+        if os.path.isfile(self.out_path):
+            self.test.logger.debug("Capture file appeared after %fs" %
+                                   (time.time() - (limit - timeout)))
+        else:
+            self.test.logger.debug("Timeout - capture file still nowhere")
+            raise Exception("Capture file did not appear within timeout")
+
     def wait_for_packet(self, timeout):
         """
         Wait for next packet captured with a timeout
@@ -144,18 +190,8 @@ class VppPGInterface(VppInterface):
         """
         limit = time.time() + timeout
         if self._pcap_reader is None:
-            self.test.logger.debug("Waiting for the capture file to appear")
-            while time.time() < limit:
-                if os.path.isfile(self.out_path):
-                    break
-                time.sleep(0)  # yield
-            if os.path.isfile(self.out_path):
-                self.test.logger.debug("Capture file appeared after %fs" %
-                                       (time.time() - (limit - timeout)))
-                self._pcap_reader = PcapReader(self.out_path)
-            else:
-                self.test.logger.debug("Timeout - capture file still nowhere")
-                raise Exception("Packet didn't arrive within timeout")
+            self.wait_for_capture_file(timeout)
+            self._pcap_reader = PcapReader(self.out_path)
 
         self.test.logger.debug("Waiting for packet")
         while time.time() < limit:
@@ -197,11 +233,11 @@ class VppPGInterface(VppInterface):
         pg_interface.enable_capture()
         self.test.pg_start()
         self.test.logger.info(self.test.vapi.cli("show trace"))
-        arp_reply = pg_interface.get_capture()
-        if arp_reply is None or len(arp_reply) == 0:
-            self.test.logger.info(
-                "No ARP received on port %s" %
-                pg_interface.name)
+        try:
+            arp_reply = pg_interface.get_capture()
+        except:
+            self.test.logger.info("No ARP received on port %s" %
+                                  pg_interface.name)
             return
         arp_reply = arp_reply[0]
         # Make Dot1AD packet content recognizable to scapy