diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index d49f3f5..6f25cff 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -485,6 +485,32 @@
     fi
 }
 
+# True if the presence of the given pattern in a log definitely indicates
+# that the test has failed. False if the presence is inconclusive.
+#
+# Inputs:
+# * $1: pattern found in the logs
+# * $TIMES_LEFT: >0 if retrying is an option
+#
+# Outputs:
+# * $outcome: set to a retry reason if the pattern is inconclusive,
+#             unchanged otherwise.
+# * Return value: 1 if the pattern is inconclusive,
+#                 0 if the failure is definitive.
+log_pattern_presence_is_conclusive() {
+    # If we've run out of attempts, then don't retry no matter what.
+    if [ $TIMES_LEFT -eq 0 ]; then
+        return 0
+    fi
+    case $1 in
+        "resend")
+            # An undesired resend may have been caused by the OS dropping or
+            # delaying a packet at an inopportune time.
+            outcome="RETRY(resend)"
+            return 1;;
+    esac
+}
+
 # fail <message>
 fail() {
     record_outcome "FAIL" "$1"
@@ -733,68 +759,12 @@
         fi
 }
 
-# Usage: run_test name [-p proxy_cmd] srv_cmd cli_cmd cli_exit [option [...]]
-# Options:  -s pattern  pattern that must be present in server output
-#           -c pattern  pattern that must be present in client output
-#           -u pattern  lines after pattern must be unique in client output
-#           -f call shell function on client output
-#           -S pattern  pattern that must be absent in server output
-#           -C pattern  pattern that must be absent in client output
-#           -U pattern  lines after pattern must be unique in server output
-#           -F call shell function on server output
-#           -g call shell function on server and client output
-run_test() {
-    NAME="$1"
-    shift 1
-
-    if is_excluded "$NAME"; then
-        SKIP_NEXT="NO"
-        # There was no request to run the test, so don't record its outcome.
-        return
-    fi
-
-    print_name "$NAME"
-
-    # Do we only run numbered tests?
-    if [ -n "$RUN_TEST_NUMBER" ]; then
-        case ",$RUN_TEST_NUMBER," in
-            *",$TESTS,"*) :;;
-            *) SKIP_NEXT="YES";;
-        esac
-    fi
-
-    # does this test use a proxy?
-    if [ "X$1" = "X-p" ]; then
-        PXY_CMD="$2"
-        shift 2
-    else
-        PXY_CMD=""
-    fi
-
-    # get commands and client output
-    SRV_CMD="$1"
-    CLI_CMD="$2"
-    CLI_EXPECT="$3"
-    shift 3
-
-    # Check if test uses files
-    case "$SRV_CMD $CLI_CMD" in
-        *data_files/*)
-            requires_config_enabled MBEDTLS_FS_IO;;
-    esac
-
-    # If the client or serve requires a ciphersuite, check that it's enabled.
-    maybe_requires_ciphersuite_enabled "$SRV_CMD" "$@"
-    maybe_requires_ciphersuite_enabled "$CLI_CMD" "$@"
-
-    # should we skip?
-    if [ "X$SKIP_NEXT" = "XYES" ]; then
-        SKIP_NEXT="NO"
-        record_outcome "SKIP"
-        SKIPS=$(( $SKIPS + 1 ))
-        return
-    fi
-
+# Analyze the commands that will be used in a test.
+#
+# Analyze and possibly instrument $PXY_CMD, $CLI_CMD, $SRV_CMD to pass
+# extra arguments or go through wrappers.
+# Set $DTLS (0=TLS, 1=DTLS).
+analyze_test_commands() {
     # update DTLS variable
     detect_dtls "$SRV_CMD"
 
@@ -848,48 +818,29 @@
             CLI_CMD="valgrind --leak-check=full $CLI_CMD"
         fi
     fi
+}
 
-    TIMES_LEFT=2
-    while [ $TIMES_LEFT -gt 0 ]; do
-        TIMES_LEFT=$(( $TIMES_LEFT - 1 ))
+# Check for failure conditions after a test case.
+#
+# Inputs from run_test:
+# * positional parameters: test options (see run_test documentation)
+# * $CLI_EXIT: client return code
+# * $CLI_EXPECT: expected client return code
+# * $SRV_RET: server return code
+# * $CLI_OUT, $SRV_OUT, $PXY_OUT: files containing client/server/proxy logs
+# * $TIMES_LEFT: if nonzero, a RETRY outcome is allowed
+#
+# Outputs:
+# * $outcome: one of PASS/RETRY*/FAIL
+check_test_failure() {
+    outcome=FAIL
 
-        # run the commands
-        if [ -n "$PXY_CMD" ]; then
-            printf "# %s\n%s\n" "$NAME" "$PXY_CMD" > $PXY_OUT
-            $PXY_CMD >> $PXY_OUT 2>&1 &
-            PXY_PID=$!
-            wait_proxy_start "$PXY_PORT" "$PXY_PID"
-        fi
-
-        check_osrv_dtls
-        printf '# %s\n%s\n' "$NAME" "$SRV_CMD" > $SRV_OUT
-        provide_input | $SRV_CMD >> $SRV_OUT 2>&1 &
-        SRV_PID=$!
-        wait_server_start "$SRV_PORT" "$SRV_PID"
-
-        printf '# %s\n%s\n' "$NAME" "$CLI_CMD" > $CLI_OUT
-        eval "$CLI_CMD" >> $CLI_OUT 2>&1 &
-        wait_client_done
-
-        sleep 0.05
-
-        # terminate the server (and the proxy)
-        kill $SRV_PID
-        wait $SRV_PID
-        SRV_RET=$?
-
-        if [ -n "$PXY_CMD" ]; then
-            kill $PXY_PID >/dev/null 2>&1
-            wait $PXY_PID
-        fi
-
-        # retry only on timeouts
-        if grep '===CLIENT_TIMEOUT===' $CLI_OUT >/dev/null; then
-            printf "RETRY "
-        else
-            TIMES_LEFT=0
-        fi
-    done
+    if [ $TIMES_LEFT -gt 0 ] &&
+       grep '===CLIENT_TIMEOUT===' $CLI_OUT >/dev/null
+    then
+        outcome="RETRY(client-timeout)"
+        return
+    fi
 
     # check if the client and server went at least to the handshake stage
     # (useful to avoid tests with only negative assertions and non-zero
@@ -948,14 +899,18 @@
 
             "-S")
                 if grep -v '^==' $SRV_OUT | grep -v 'Serious error when reading debug info' | grep "$2" >/dev/null; then
-                    fail "pattern '$2' MUST NOT be present in the Server output"
+                    if log_pattern_presence_is_conclusive "$2"; then
+                        fail "pattern '$2' MUST NOT be present in the Server output"
+                    fi
                     return
                 fi
                 ;;
 
             "-C")
                 if grep -v '^==' $CLI_OUT | grep -v 'Serious error when reading debug info' | grep "$2" >/dev/null; then
-                    fail "pattern '$2' MUST NOT be present in the Client output"
+                    if log_pattern_presence_is_conclusive "$2"; then
+                        fail "pattern '$2' MUST NOT be present in the Client output"
+                    fi
                     return
                 fi
                 ;;
@@ -1019,6 +974,131 @@
     fi
 
     # if we're here, everything is ok
+    outcome=PASS
+}
+
+# Run the current test case: start the server and if applicable the proxy, run
+# the client, wait for all processes to finish or time out.
+#
+# Inputs:
+# * $NAME: test case name
+# * $CLI_CMD, $SRV_CMD, $PXY_CMD: commands to run
+# * $CLI_OUT, $SRV_OUT, $PXY_OUT: files to contain client/server/proxy logs
+#
+# Outputs:
+# * $CLI_EXIT: client return code
+# * $SRV_RET: server return code
+do_run_test_once() {
+    # run the commands
+    if [ -n "$PXY_CMD" ]; then
+        printf "# %s\n%s\n" "$NAME" "$PXY_CMD" > $PXY_OUT
+        $PXY_CMD >> $PXY_OUT 2>&1 &
+        PXY_PID=$!
+        wait_proxy_start "$PXY_PORT" "$PXY_PID"
+    fi
+
+    check_osrv_dtls
+    printf '# %s\n%s\n' "$NAME" "$SRV_CMD" > $SRV_OUT
+    provide_input | $SRV_CMD >> $SRV_OUT 2>&1 &
+    SRV_PID=$!
+    wait_server_start "$SRV_PORT" "$SRV_PID"
+
+    printf '# %s\n%s\n' "$NAME" "$CLI_CMD" > $CLI_OUT
+    eval "$CLI_CMD" >> $CLI_OUT 2>&1 &
+    wait_client_done
+
+    sleep 0.05
+
+    # terminate the server (and the proxy)
+    kill $SRV_PID
+    wait $SRV_PID
+    SRV_RET=$?
+
+    if [ -n "$PXY_CMD" ]; then
+        kill $PXY_PID >/dev/null 2>&1
+        wait $PXY_PID
+    fi
+}
+
+# Usage: run_test name [-p proxy_cmd] srv_cmd cli_cmd cli_exit [option [...]]
+# Options:  -s pattern  pattern that must be present in server output
+#           -c pattern  pattern that must be present in client output
+#           -u pattern  lines after pattern must be unique in client output
+#           -f call shell function on client output
+#           -S pattern  pattern that must be absent in server output
+#           -C pattern  pattern that must be absent in client output
+#           -U pattern  lines after pattern must be unique in server output
+#           -F call shell function on server output
+#           -g call shell function on server and client output
+run_test() {
+    NAME="$1"
+    shift 1
+
+    if is_excluded "$NAME"; then
+        SKIP_NEXT="NO"
+        # There was no request to run the test, so don't record its outcome.
+        return
+    fi
+
+    print_name "$NAME"
+
+    # Do we only run numbered tests?
+    if [ -n "$RUN_TEST_NUMBER" ]; then
+        case ",$RUN_TEST_NUMBER," in
+            *",$TESTS,"*) :;;
+            *) SKIP_NEXT="YES";;
+        esac
+    fi
+
+    # does this test use a proxy?
+    if [ "X$1" = "X-p" ]; then
+        PXY_CMD="$2"
+        shift 2
+    else
+        PXY_CMD=""
+    fi
+
+    # get commands and client output
+    SRV_CMD="$1"
+    CLI_CMD="$2"
+    CLI_EXPECT="$3"
+    shift 3
+
+    # Check if test uses files
+    case "$SRV_CMD $CLI_CMD" in
+        *data_files/*)
+            requires_config_enabled MBEDTLS_FS_IO;;
+    esac
+
+    # If the client or serve requires a ciphersuite, check that it's enabled.
+    maybe_requires_ciphersuite_enabled "$SRV_CMD" "$@"
+    maybe_requires_ciphersuite_enabled "$CLI_CMD" "$@"
+
+    # should we skip?
+    if [ "X$SKIP_NEXT" = "XYES" ]; then
+        SKIP_NEXT="NO"
+        record_outcome "SKIP"
+        SKIPS=$(( $SKIPS + 1 ))
+        return
+    fi
+
+    analyze_test_commands "$@"
+
+    TIMES_LEFT=2
+    while [ $TIMES_LEFT -gt 0 ]; do
+        TIMES_LEFT=$(( $TIMES_LEFT - 1 ))
+
+        do_run_test_once
+
+        check_test_failure "$@"
+        case $outcome in
+            PASS) break;;
+            RETRY*) printf "$outcome ";;
+            FAIL) return;;
+        esac
+    done
+
+    # If we get this far, the test case passed.
     record_outcome "PASS"
     if [ "$PRESERVE_LOGS" -gt 0 ]; then
         mv $SRV_OUT o-srv-${TESTS}.log