Add a test for spinning on no-change screen updates

src/tests/Makefile.am

@@ -22,6 +22,7 @@ displaytests = \
 	emulation-cursor-motion.test \
 	emulation-multiline-scroll.test \
 	emulation-wrap-across-frames.test \
+	network-no-diff.test \
 	prediction-unicode.test \
 	pty-deadlock.test \
 	repeat.test \

src/tests/e2e-test-server

@@ -29,6 +29,11 @@ fi
 # run harnessed command
 eval "$@"
 testret=$?
+# Capture mosh-server runtime if possible.
+runtime=$(ps -o time= $PPID 2>/dev/null)
+if [ $? -ne 0 ]; then # Cygwin...
+    runtime=-
+fi
 # Wait for tmux client screen to become up to date.
 sleep 1
 printf "@@@ server complete @@@" >&2
@@ -53,6 +58,8 @@ if ! tmux save-buffer "$testname.capture"; then
     printf "tmux save-buffer failed, erroring test\n" >&2
     exit 99
 fi
+# Dump runtime into tmux log.
+printf "@@@ runtime %s @@@\n" "$runtime"
 # return useful exitstatus from harnessed command
 if [ $testret -ne 0 ]; then
     exit 1

src/tests/network-no-diff.test

@@ -0,0 +1,60 @@
+#!/bin/sh
+
+#
+# This is a regression test to ensure that Mosh does not spin
+# on updates that do not actually change the framebuffer.
+#
+
+# shellcheck source=e2e-test-subrs
+. "$(dirname "$0")/e2e-test-subrs"
+PATH=$PATH:.:$srcdir
+# Top-level wrapper.
+if [ $# -eq 0 ]; then
+    e2e-test "$0" baseline post
+    exit
+fi
+
+# OK, we have arguments, we're one of the test hooks.
+if [ $# -ne 1 ]; then
+    fail "bad arguments %s\n" "$@"
+fi
+
+baseline()
+{
+    # Generate updates that don't change the screen
+    i=0
+    while [ $i -lt 10 ]; do
+	printf 'x\b'
+	i=$((i + 1))
+	sleep 1
+    done
+}
+
+post()
+{
+    # Extract server run time.
+    runtime=$(sed -E -n 's/.*@@@ runtime: (.*) @@@.*/\1/p' "$(basename "$0").d/baseline.tmux.log")
+
+    # If this system can't actually report runtime, bail.
+    if [ -z "$runtime" ] || [ "$runtime" -eq "-" ]; then
+	exit 0
+    fi
+
+    # If we ran for more than one second, fail.
+    seconds=${runtime##*:}
+    bigger=${runtime%:*}
+    onesec=$(echo "$seconds >= 1" | bc)
+    if [ "$onesec" -eq 1 ] || [ "$bigger" -ne 0 ]; then
+	exit 1
+    fi
+    exit 0
+}
+
+case $1 in
+    baseline)
+	baseline;;
+    post)
+	post;;
+    *)
+	fail "unknown test argument %s\n" "$1";;
+esac