diff --git a/src/cmd/ksh93/tests/arrays.sh b/src/cmd/ksh93/tests/arrays.sh
index f24b5578bc2f..4e27367f2089 100755
--- a/src/cmd/ksh93/tests/arrays.sh
+++ b/src/cmd/ksh93/tests/arrays.sh
@@ -524,6 +524,7 @@ typeset -m 'a[0]=a[1]'
 typeset -m 'a[1]=j'
 [[ ${a[@]} == 'bb aa cc' ]] || err_exit 'moving index array elements not working'
 unset a j
+[[ $(typeset -p a) ]] && err_exit 'unset associative array after typeset -m not working'
 
 typeset -A a=( [0]="aa" [1]="bb" [2]="cc" )
 typeset -m 'j=a[0]'
diff --git a/src/cmd/ksh93/tests/arrays2.sh b/src/cmd/ksh93/tests/arrays2.sh
index 23e1d8247479..4701565fdb9b 100755
--- a/src/cmd/ksh93/tests/arrays2.sh
+++ b/src/cmd/ksh93/tests/arrays2.sh
@@ -224,6 +224,15 @@ print -v cx > /dev/null
 print -v cx | read -C l 2> /dev/null || err_exit 'read -C fails from output of print -v'
 ((SHOPT_FIXEDARRAY)) && [[ ${cx%cx=} != "${l%l=}" ]] && err_exit 'print -v for compound variable with fixed 2d array not working'
 
+unset foo
+typeset -A foo
+typeset -A foo[bar]
+foo[bar][x]=2
+(( foo[bar][x]++ ))
+exp=3
+[[ ${foo[bar][x]} == $exp ]] || err_ext "subscript gets added incorrectly to an associative array when ++ operator is called" \
+	"(expected '$exp', got '${foo[bar][x]}')"
+
 # ======
 # Multidimensional arrays with an unset method shouldn't cause a crash.
 # The test itself must be run inside of a function.
diff --git a/src/cmd/ksh93/tests/basic.sh b/src/cmd/ksh93/tests/basic.sh
index 18fd83dc1576..7d8f52a5319f 100755
--- a/src/cmd/ksh93/tests/basic.sh
+++ b/src/cmd/ksh93/tests/basic.sh
@@ -419,8 +419,16 @@ unset foo
 unset foo
 foo=$(false) > /dev/null && err_exit 'failed command substitution with redirection not returning false'
 expected=foreback
+got=`print -n fore; (sleep 2;print back)&`
+[[ $got == $expected ]] || err_exit "\`\` command substitution background process output error (expected '$expected', got '$got')"
 got=$(print -n fore; (sleep .2;print back)&)
-[[ $got == $expected ]] || err_exit "command substitution background process output error -- got '$got', expected '$expected'"
+[[ $got == $expected ]] || err_exit "\$() command substitution background process output error (expected '$expected', got '$got')"
+got=${ print -n fore; (sleep 2;print back)& }
+[[ $got == $expected ]] || err_exit "\${} shared-state command substitution background process output error (expected '$expected', got '$got')"
+function abc { sleep 2; print back; }
+function abcd { abc & }
+got=$(print -n fore;abcd)
+[[ $got == $expected ]] || err_exit "\$() command substitution background with function process output error (expected '$expected', got '$got')"
 
 for false in false $binfalse
 do	x=$($false) && err_exit "x=\$($false) should fail"
@@ -790,5 +798,46 @@ trap - DEBUG  # bug compat
 [[ $got == "$exp" ]] || err_exit "DEBUG trap did not trigger return from POSIX function on status 255" \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 
+# ======
+# In ksh93v- and ksh2020 EXIT traps don't work in forked subshells
+# https://github.com/att/ast/issues/1452
+exp="forked subshell EXIT trap okay"
+got="$(ulimit -t unlimited; trap 'echo forked subshell EXIT trap okay' EXIT)"
+[[ $got == $exp ]] || err_exit "EXIT trap did not trigger in forked subshell" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
+exp="virtual subshell EXIT trap okay"
+got="$(trap 'echo virtual subshell EXIT trap okay' EXIT)"
+[[ $got == $exp ]] || err_exit "EXIT trap did not trigger in virtual subshell" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
+# ======
+# Regression test for https://github.com/att/ast/issues/1403
+for t in {A..Z}; do
+	$SHELL -c "trap - $t 2> /dev/null"
+	[[ $? == 1 ]] || err_exit "'trap' throws segfault when given invalid signal name '$t'"
+done
+
+# ======
+# Is an invalid flag handled correctly?
+# ksh2020 regression: https://github.com/att/ast/issues/1284
+actual=$($SHELL --verson 2>&1)
+actual_status=$?
+expect='ksh: verson: bad option(s)'
+expect_status=2
+[[ "$actual" == ${expect}* ]] || err_exit "failed to get version string" \
+	"(expected $(printf %q ${expect}*), got $(printf %q "$actual"))"
+[[ $actual_status == $expect_status ]] ||
+	err_exit "wrong exit status (expected '$expect_status', got '$actual_status')"
+
+# ======
+# Test for illegal seek error (ksh93v- regression)
+# https://www.mail-archive.com/ast-users@lists.research.att.com/msg00816.html
+exp='1
+2'
+got="$(join <(printf '%d\n' 1 2) <(printf '%d\n' 1 2))"
+[[ $exp == $got ]] || err_exit "pipeline fails with illegal seek error" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))
diff --git a/src/cmd/ksh93/tests/bracket.sh b/src/cmd/ksh93/tests/bracket.sh
index 4d7d6b00631d..95771aee70d9 100755
--- a/src/cmd/ksh93/tests/bracket.sh
+++ b/src/cmd/ksh93/tests/bracket.sh
@@ -408,5 +408,13 @@ do	unset var
 	[[ -n ${var+s} ]] || err_exit "[[ -n \${var+s} ]] should be true for empty var with attribute -$flag"
 done
 
+# ======
+# Tests from ksh93v- for the -eq operator
+[[ 010 -eq 10 ]] || err_exit '010 is not 10 in [[...]]'
+
+unset foo
+foo=10
+([[ foo -eq 10 ]]) || err_exit 'foo -eq 10 fails in [[...]] with foo=10'
+
 # ======
 exit $((Errors<125?Errors:125))
diff --git a/src/cmd/ksh93/tests/builtins.sh b/src/cmd/ksh93/tests/builtins.sh
index 76630e31f7e9..5e7330f2b628 100755
--- a/src/cmd/ksh93/tests/builtins.sh
+++ b/src/cmd/ksh93/tests/builtins.sh
@@ -686,11 +686,6 @@ then	(
 fi
 cd "$tmp"
 
-$SHELL +E -i 2>/dev/null <<- \! && err_exit 'interactive shell should not exit 0 after false'
-	false
-	exit
-!
-
 if	kill -L > /dev/null 2>&1
 then	[[ $(kill -l HUP) == "$(kill -L HUP)" ]] || err_exit 'kill -l and kill -L are not the same when given a signal name'
 	[[ $(kill -l 9) == "$(kill -L 9)" ]] || err_exit 'kill -l and kill -L are not the same when given a signal number'
@@ -974,7 +969,7 @@ fi
 EOF
 "$SHELL" -i "$sleepsig" 2> /dev/null || err_exit "'sleep -s' doesn't work with intervals of more than 30 seconds"
 
-# ==========
+# ======
 # Builtins should handle unrecognized options correctly
 while IFS= read -r bltin <&3
 do	case $bltin in
@@ -1013,5 +1008,42 @@ then	got=$( { "$SHELL" -c '
 		"(got status $e$( ((e>128)) && print -n / && kill -l "$e"), $(printf %q "$got"))"
 fi
 
+# ======
+# Regression test for https://github.com/att/ast/issues/1402
+#
+# We throw away stderr because we only want the value of '$t', not the error text from running
+# 'command' with an invalid flag.
+exp='good'
+got=$($SHELL -c 't=good; t=bad command -@; print $t' 2>/dev/null)
+[[ $exp == $got ]] || err_exit "temp var assignment with 'command'" \
+	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
+
+# ======
+# Regression test for https://github.com/att/ast/issues/949
+foo_script='#!/bin/sh
+exit 0'
+echo "$foo_script" > "$tmp/foo1.sh"
+echo "$foo_script" > "$tmp/foo2.sh"
+builtin chmod
+chmod +x "$tmp/foo1.sh" "$tmp/foo2.sh"
+$SHELL "$tmp/foo1.sh" || err_exit "builtin 'chmod +x' doesn't work on first script"
+$SHELL "$tmp/foo2.sh" || err_exit "builtin 'chmod +x' doesn't work on second script"
+
+# ======
+# In ksh93v- 2013-10-10 alpha cd doesn't fail on directories without execute permission.
+# Additionally, ksh93v- added a regression test for attempting to use cd on a file.
+mkdir "$tmp/noexecute"
+chmod -x "$tmp/noexecute"
+$SHELL -c "cd $tmp/noexecute" 2> /dev/null && err_exit "'cd' on directories without an execute bit doesn't fail"
+touch "$tmp/notadir"
+$SHELL -c "cd $tmp/notadir" 2> /dev/null && err_exit "'cd' on a normal file doesn't fail"
+
+# ======
+# 'kill %' should fail with exit status 1
+{ $SHELL -c 'kill %' ;} 2> /dev/null
+got=$?
+exp=1
+[[ $got == $exp ]] || err_exit "'kill %' has the wrong exit status (expected '$exp'; got '$got')"
+
 # ======
 exit $((Errors<125?Errors:125))
diff --git a/src/cmd/ksh93/tests/case.sh b/src/cmd/ksh93/tests/case.sh
index 84c6b42b66be..f28d56e18c29 100755
--- a/src/cmd/ksh93/tests/case.sh
+++ b/src/cmd/ksh93/tests/case.sh
@@ -102,5 +102,11 @@ got=$(eval 'case x in (if);; esac' 2>&1) || err_exit "'(' + 'if' as first patter
 got=$(eval 'case x in foo);; if);; esac' 2>&1) || err_exit "'if' as nth pattern fails: got $(printf %q "$got")"
 got=$(eval 'case x in (foo);; (if);; esac' 2>&1) || err_exit "'(' + 'if' as nth pattern fails: got $(printf %q "$got")"
 
+# ======
+# Verify an invalid character class name is handled without a SIGSEGV or similar failure
+# https://github.com/att/ast/issues/1409
+got="$($SHELL -c 'case x in [x[:bogus:]]) echo x ;; esac')"
+[[ -z $got ]] || err_exit "invalid char class name (got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))
diff --git a/src/cmd/ksh93/tests/exit.sh b/src/cmd/ksh93/tests/exit.sh
index a6ca0647e97e..1940e7f4213c 100755
--- a/src/cmd/ksh93/tests/exit.sh
+++ b/src/cmd/ksh93/tests/exit.sh
@@ -76,4 +76,64 @@ cd /
 cd ~- || err_exit "cd back failed"
 $SHELL -c 'builtin -f cmd getconf; getconf --"?-version"; exit 0' >/dev/null 2>&1 || err_exit 'ksh plugin exit failed -- was ksh built with CCFLAGS+=$(CC.EXPORT.DYNAMIC)?'
 
+# ======
+# Verify the 'exit' command behaves as expected
+
+got=$($SHELL -c 'exit' 2>&1)
+status=$?
+exp=0
+[[ -z $got ]] || err_exit 'bare exit' \
+	"(got $(printf %q "$got"))"
+[[ $exp == $status ]] || err_exit 'bare exit' \
+	"(expected '$exp', got '$status')"
+
+got=$($SHELL -c 'exit 0' 2>&1)
+status=$?
+exp=0
+[[ -z $got ]] || err_exit 'exit 0' \
+	"(got $(printf %q "$got"))"
+[[ $exp == $status ]] || err_exit 'exit 0' \
+	"(expected '$exp', got '$status')"
+
+got=$($SHELL -c 'exit 1' 2>&1)
+status=$?
+exp=1
+[[ -z $got ]] || err_exit 'exit 1' \
+	"(got $(printf %q "$got"))"
+[[ $exp == $status ]] || err_exit 'exit 1' \
+	"(expected '$exp', got '$status')"
+
+got=$($SHELL -c 'function e37 { return 37; } ; e37' 2>&1)
+status=$?
+exp=37
+[[ -z $got ]] || err_exit 'exit 37' \
+	"(got $(printf %q "$got"))"
+[[ $exp == $status ]] || err_exit 'exit 37' \
+	"(expected '$exp', got '$status')"
+
+got=$($SHELL -c 'exit -1' 2>&1)
+status=$?
+exp=255
+[[ -z $got ]] || err_exit 'exit -1' \
+	"(got $(printf %q "$got"))"
+[[ $exp == $status ]] || err_exit 'exit -1' \
+	"(expected '$exp', got '$status')"
+
+got=$($SHELL -c 'exit -2' 2>&1)
+status=$?
+exp=254
+[[ -z $got ]] || err_exit 'exit -2' \
+	"(got $(printf %q "$got"))"
+[[ $exp == $status ]] || err_exit 'exit -2' \
+	"(expected '$exp', got '$status')"
+
+$SHELL +E -i 2>/dev/null <<- \! && err_exit 'interactive shell should not exit 0 after false'
+	false
+	exit
+!
+status=$?
+exp=1
+[[ $exp == $status ]] || err_exit 'bare exit after false' \
+	"(expected '$exp', got '$status')"
+
 exit $((Errors<125?Errors:125))
diff --git a/src/cmd/ksh93/tests/io.sh b/src/cmd/ksh93/tests/io.sh
index ace60fe040a7..3a73d7be46df 100755
--- a/src/cmd/ksh93/tests/io.sh
+++ b/src/cmd/ksh93/tests/io.sh
@@ -715,5 +715,23 @@ got=$(export tmp; "$SHELL" -ec \
 (redirect {v}>$tmp/v.out; echo ok2 >&$v) 2>/dev/null
 [[ -r $tmp/v.out && $(<$tmp/v.out) == ok2 ]] || err_exit 'redirect {varname}>file not working in a subshell'
 
+# ======
+# Regression test for a process substitution hang in ksh93v- 2013-10-10 alpha
+{
+	producer() {
+		for ((i = 0; i < 20000; i++ )) do
+			print xxxxx${i}xxxxx
+		done
+	}
+	consumer() {
+		while read var; do
+			print ${var}
+		done < ${1}
+	}
+	consumer <(producer) > /dev/null
+} & pid=$!
+(sleep 5; kill -HUP $pid) 2> /dev/null &
+wait $pid 2> /dev/null || err_exit "process substitution hangs"
+
 # ======
 exit $((Errors<125?Errors:125))
diff --git a/src/cmd/ksh93/tests/math.sh b/src/cmd/ksh93/tests/math.sh
index 2e4c948b97ab..b13e6c35f2ee 100755
--- a/src/cmd/ksh93/tests/math.sh
+++ b/src/cmd/ksh93/tests/math.sh
@@ -260,5 +260,12 @@ unset x
 [[ $(typeset -lE 0 x=5.67; typeset -p x) == 'typeset -l -E 0 x=6' ]] || err_exit 'typeset -lE 0 with assignment failed to round.'
 [[ $(typeset -lX 0 x=5.67; typeset -p x) == 'typeset -l -X 0 x=0x1p+2' ]] || err_exit 'typeset -lX 0 with assignment failed to round.'
 
+# ======
+# typeset -s used without -i shouldn't set foo to garbage
+exp=30000
+got="$(typeset -s foo=30000; echo $foo)"
+[[ $exp == $got ]] || err_exit "unexpected output from typeset -s without -i" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))
diff --git a/src/cmd/ksh93/tests/variables.sh b/src/cmd/ksh93/tests/variables.sh
index 727160c81ef8..bdb40b8e308f 100755
--- a/src/cmd/ksh93/tests/variables.sh
+++ b/src/cmd/ksh93/tests/variables.sh
@@ -1258,5 +1258,13 @@ exp='foo/foobar/fool'
 got=$(IFS=/; foo=bar foobar=fbar fool=pity; print -r -- "${!foo*}")
 [[ $got == "$exp" ]] || err_exit "\${!foo*}: expected $(printf %q "$exp"), got $(printf %q "$got")"
 
+# ======
+# In ksh93v- ${.sh.subshell} is unset by the $PS4 prompt
+# https://github.com/att/ast/issues/1092
+exp='0'
+got="$($SHELL -c 'PS4="${.sh.subshell}"; echo ${.sh.subshell}')"
+[[ "$exp" == "$got" ]] || err_exit "\${.sh.subshell} is wrongly unset in the \$PS4 prompt" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))