diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index 98db65f2..b15e29c3 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -16,3 +16,4 @@ jobs:
       - name: check that implementations.json is valid
         if: success() || failure() # run this step even if the previous one failed
         run: python implementations.py
+      - uses: ludeeus/action-shellcheck@master
diff --git a/certs.sh b/certs.sh
index 174a120a..f7c19f53 100755
--- a/certs.sh
+++ b/certs.sh
@@ -19,7 +19,7 @@ openssl req -x509 -sha256 -nodes -days 10 -key "$CERTDIR"/ca_0.key \
   -subj "/O=interop runner Root Certificate Authority/" \
   -config cert_config.txt \
   -extensions v3_ca \
-  2> /dev/null
+  2>/dev/null
 
 # Inflate certificate for the amplification test
 fakedns=""
@@ -39,21 +39,21 @@ for i in $(seq 1 "$CHAINLEN"); do
   openssl ecparam -name prime256v1 -genkey -out "$CERTDIR"/ca_"$i".key
   openssl req -out "$CERTDIR"/cert.csr -new -key "$CERTDIR"/ca_"$i".key -nodes \
     -subj "/O=$SUBJ/" \
-    2> /dev/null
+    2>/dev/null
 
   # Sign the certificate
-  j=$((i-1))
+  j=$((i - 1))
   if [[ $i < "$CHAINLEN" ]]; then
     openssl x509 -req -sha256 -days 10 -in "$CERTDIR"/cert.csr -out "$CERTDIR"/cert_"$i".pem \
       -CA "$CERTDIR"/cert_"$j".pem -CAkey "$CERTDIR"/ca_"$j".key -CAcreateserial \
       -extfile cert_config.txt \
       -extensions v3_ca \
-      2> /dev/null
+      2>/dev/null
   else
     openssl x509 -req -sha256 -days 10 -in "$CERTDIR"/cert.csr -out "$CERTDIR"/cert_"$i".pem \
       -CA "$CERTDIR"/cert_"$j".pem -CAkey "$CERTDIR"/ca_"$j".key -CAcreateserial \
-      -extfile <(printf "subjectAltName=DNS:server,DNS:server4,DNS:server6,DNS:server46$fakedns") \
-      2> /dev/null
+      -extfile <(printf "subjectAltName=DNS:server,DNS:server4,DNS:server6,DNS:server46%s" "$fakedns") \
+      2>/dev/null
   fi
 done
 
@@ -62,7 +62,7 @@ cp "$CERTDIR"/ca_"$CHAINLEN".key "$CERTDIR"/priv.key
 
 # combine certificates
 for i in $(seq "$CHAINLEN" -1 1); do
-  cat "$CERTDIR"/cert_"$i".pem >> "$CERTDIR"/cert.pem
+  cat "$CERTDIR"/cert_"$i".pem >>"$CERTDIR"/cert.pem
   rm "$CERTDIR"/cert_"$i".pem "$CERTDIR"/ca_"$i".key
 done
 rm -f "$CERTDIR"/*.srl "$CERTDIR"/ca_0.key "$CERTDIR"/cert.csr
diff --git a/interop.py b/interop.py
index 41fd699f..d6b27cea 100644
--- a/interop.py
+++ b/interop.py
@@ -180,27 +180,29 @@ def _check_impl_is_compliant(self, name: str) -> bool:
     def _postprocess_results(self):
         clients = list(set(client for client, _ in self._client_server_pairs))
         servers = list(set(server for _, server in self._client_server_pairs))
-        # If a client failed a test against all servers, make the test unsupported for the client
         questionable = [TestResult.FAILED, TestResult.UNSUPPORTED]
-        for c in set(clients) - set(self._no_auto_unsupported):
-            for t in self._tests:
-                if all(self.test_results[s][c][t] in questionable for s in servers):
-                    print(
-                        f'Client {c} failed test "{t.name()}" against all servers, '
-                        + 'marking the entire test as "unsupported"'
-                    )
-                    for s in servers:
-                        self.test_results[s][c][t] = TestResult.UNSUPPORTED
+        # If a client failed a test against all servers, make the test unsupported for the client
+        if len(servers) > 1:
+            for c in set(clients) - set(self._no_auto_unsupported):
+                for t in self._tests:
+                    if all(self.test_results[s][c][t] in questionable for s in servers):
+                        print(
+                            f"Client {c} failed or did not support test {t.name()} "
+                            + 'against all servers, marking the entire test as "unsupported"'
+                        )
+                        for s in servers:
+                            self.test_results[s][c][t] = TestResult.UNSUPPORTED
         # If a server failed a test against all clients, make the test unsupported for the server
-        for s in set(servers) - set(self._no_auto_unsupported):
-            for t in self._tests:
-                if all(self.test_results[s][c][t] in questionable for c in clients):
-                    print(
-                        f'Server {s} failed test "{t.name()}" against all clients, '
-                        + 'marking the entire test as "unsupported"'
-                    )
-                    for c in clients:
-                        self.test_results[s][c][t] = TestResult.UNSUPPORTED
+        if len(clients) > 1:
+            for s in set(servers) - set(self._no_auto_unsupported):
+                for t in self._tests:
+                    if all(self.test_results[s][c][t] in questionable for c in clients):
+                        print(
+                            f"Server {s} failed or did not support test {t.name()} "
+                            + 'against all clients, marking the entire test as "unsupported"'
+                        )
+                        for c in clients:
+                            self.test_results[s][c][t] = TestResult.UNSUPPORTED
 
     def _print_results(self):
         """print the interop table"""
diff --git a/testcases.py b/testcases.py
index ced187ea..b38c24d9 100644
--- a/testcases.py
+++ b/testcases.py
@@ -302,6 +302,8 @@ def get_paths(self):
 
     @abc.abstractmethod
     def check(self) -> TestResult:
+        self._client_trace()
+        self._server_trace()
         pass
 
 
@@ -338,6 +340,7 @@ def get_paths(self):
         return [""]
 
     def check(self) -> TestResult:
+        super().check()
         tr = self._client_trace()
         initials = tr.get_initial(Direction.FROM_CLIENT)
         dcid = ""
@@ -373,6 +376,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         if not self._check_version_and_files():
             return TestResult.FAILED
         if self._retry_sent():
@@ -408,6 +412,7 @@ def scenario() -> str:
         return "simple-p2p --delay=750ms --bandwidth=10Mbps --queue=25"
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
@@ -453,6 +458,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
@@ -484,6 +490,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
@@ -528,6 +535,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         if not self._keylog_file():
             logging.info("Can't check test result. SSLKEYLOG required.")
             return TestResult.UNSUPPORTED
@@ -609,6 +617,7 @@ def _check_trace(self) -> bool:
         return False
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
@@ -641,6 +650,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         if not self._keylog_file():
             logging.info("Can't check test result. SSLKEYLOG required.")
             return TestResult.UNSUPPORTED
@@ -702,6 +712,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 2:
             logging.info("Expected exactly 2 handshakes. Got: %d", num_handshakes)
@@ -744,6 +755,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
@@ -787,6 +799,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         if not self._keylog_file():
             logging.info("Can't check test result. SSLKEYLOG required.")
             return TestResult.UNSUPPORTED
@@ -898,6 +911,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
@@ -931,6 +945,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         if not self._keylog_file():
             logging.info("Can't check test result. SSLKEYLOG required.")
             return TestResult.UNSUPPORTED
@@ -1026,6 +1041,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != self._num_runs:
             logging.info(
@@ -1065,6 +1081,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
@@ -1144,6 +1161,7 @@ def _check_ack_ecn(self, tr) -> bool:
         return False
 
     def check(self) -> TestResult:
+        super().check()
         if not self._keylog_file():
             logging.info("Can't check test result. SSLKEYLOG required.")
             return TestResult.UNSUPPORTED
@@ -1242,6 +1260,7 @@ def _path(p: List) -> Tuple[str, int, str, int]:
         )
 
     def check(self) -> TestResult:
+        super().check()
         if not self._keylog_file():
             logging.info("Can't check test result. SSLKEYLOG required.")
             return TestResult.UNSUPPORTED
@@ -1330,7 +1349,34 @@ def scenario() -> str:
         )
 
     def check(self) -> TestResult:
-        return super(TestCaseAddressRebinding, self).check()
+        super().check()
+        if not self._keylog_file():
+            logging.info("Can't check test result. SSLKEYLOG required.")
+            return TestResult.UNSUPPORTED
+
+        tr_server = self._server_trace()._get_packets(
+            self._server_trace()._get_direction_filter(Direction.FROM_SERVER) + " quic"
+        )
+
+        ips = set()
+        for p in tr_server:
+            ip_vers = "ip"
+            if "IPV6" in str(p.layers):
+                ip_vers = "ipv6"
+            ips.add(getattr(p[ip_vers], "dst"))
+
+        logging.info("Server saw these client addresses: %s", ips)
+        if len(ips) <= 1:
+            logging.info(
+                "Server saw only a single client IP address in use; test broken?"
+            )
+            return TestResult.FAILED
+
+        result = super(TestCaseAddressRebinding, self).check()
+        if result != TestResult.SUCCEEDED:
+            return result
+
+        return TestResult.SUCCEEDED
 
 
 class TestCaseIPv6(TestCaseTransfer):
@@ -1362,6 +1408,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         result = super(TestCaseIPv6, self).check()
         if result != TestResult.SUCCEEDED:
             return result
@@ -1413,6 +1460,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         # The parent check() method ensures that the client changed addresses
         # and that PATH_CHALLENGE/RESPONSE frames were sent and received
         result = super(TestCaseConnectionMigration, self).check()
@@ -1471,6 +1519,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         # Client should initially send QUIC v1 packet.  It may send
         # QUIC v2 packet.
         versions = self._get_packet_versions(
@@ -1574,6 +1623,7 @@ def get_paths(self):
         return self._files
 
     def check(self) -> TestResult:
+        super().check()
         num_handshakes = self._count_handshakes()
         if num_handshakes != 1:
             logging.info("Expected exactly 1 handshake. Got: %d", num_handshakes)
diff --git a/web/cleanup.sh b/web/cleanup.sh
index 758205ec..b7c4e586 100755
--- a/web/cleanup.sh
+++ b/web/cleanup.sh
@@ -3,21 +3,21 @@
 # This script is used to delete old logs from the log directory.
 # It removes log directories it deletes from logs.json.
 
-die () {
+die() {
   echo "$0 <directory> <max age (in days)>"
   exit 1
 }
 
-if [ -z $1 ] || [ -z $2 ] ; then
+if [ -z "$1" ] || [ -z "$2" ]; then
   die
 fi
 
 LOGDIR=$1
 AGE=$2
 
-find $LOGDIR -maxdepth 1 -type d -mtime +$AGE | while read line; do
-  DIR=`basename $line`
+find "$LOGDIR" -maxdepth 1 -type d -mtime "+$AGE" | while read -r line; do
+  DIR=$(basename "$line")
   echo "Deleting $DIR"
-  jq ". - [ \"$DIR\" ]" $LOGDIR/logs.json | sponge $LOGDIR/logs.json
-  rm -rf $line
+  jq ". - [ \"$DIR\" ]" "$LOGDIR/logs.json" | sponge "$LOGDIR/logs.json"
+  rm -rf "$line"
 done