diff --git a/spec/test-builtin.test.sh b/spec/test-builtin.test.sh
@@ -4,6 +4,22 @@
 # - osh is using the external binary.
 # - because ! -a -o ( ) are the same, we can share logic with [[.

+### test with extra args is syntax error
+test -n x ]
+echo status=$?
+test -n x y
+echo status=$?
+# stdout-json: "status=2\nstatus=2\n"
+
+### ] syntax errors
+[ -n x  # missing ]
+echo status=$?
+[ -n x ] y  # extra arg after ]
+echo status=$?
+[ -n x y  # extra arg
+echo status=$?
+# stdout-json: "status=2\nstatus=2\nstatus=2\n"
+
 ### empty string is false.  Equivalent to -n.
 test 'a'  && echo true
 test ''   || echo false
@@ -18,6 +34,11 @@ test -n ''   || echo false
 [ -z '' -a ! -z x ] && echo true
 # stdout: true

+### test whether == is empty
+[ == ] && echo true
+[ -n == ] && echo true
+# stdout-json: "true\ntrue\n"
+
 ### ( )
 [ -z '' -a '(' ! -z x ')' ] && echo true
 # stdout: true
@@ -26,3 +47,52 @@ test -n ''   || echo false
 command [ --version
 command [ -z '' -a '(' ! -z x ')' ] && echo true
 # stdout: true
+
+### == is alias for =
+[ a = a ] && echo true
+[ a == a ] && echo true
+# stdout-json: "true\ntrue\n"
+# BUG dash stdout-json: "true\n"
+# BUG dash status: 2
+
+### [ with op variable
+# OK -- parsed AFTER evaluation of vars
+op='='
+[ a $op a ] && echo true
+[ a $op b ] || echo false
+# status: 0
+# stdout-json: "true\nfalse\n"
+
+### [ with unquoted empty var
+empty=''
+[ $empty = '' ] && echo true
+# status: 2
+
+### [ compare with literal -f
+# Hm this is the same
+var=-f
+[ $var = -f ] && echo true
+[ '-f' = $var ] && echo true
+# stdout-json: "true\ntrue\n"
+
+### [ '(' ] is treated as literal
+[ '(' ]
+echo status=$?
+# stdout: status=0
+
+### [ '(' foo ] is runtime syntax error
+[ '(' foo ]
+echo status=$?
+# stdout: status=2
+
+### empty ! is treated as literal
+[ '!' ]
+echo status=$?
+# stdout: status=0
+
+### -z '>' implies two token lookahead
+[ -z ] && echo true  # -z is operand
+[ -z '>' ] || echo false  # -z is operator
+[ -z '>' -- ] && echo true  # -z is operand
+# stdout-json: "true\nfalse\ntrue\n"
+
diff --git a/test/spec.sh b/test/spec.sh
@@ -237,9 +237,8 @@ if_() {
    ${REF_SHELLS[@]} $ZSH $OSH "$@"
 }

-# NOTE: osh uses external test!  But that's OK for now.
 test-builtin() {
-  sh-spec spec/test-builtin.test.sh --osh-failures-allowed 1 \
+  sh-spec spec/test-builtin.test.sh --osh-failures-allowed 10 \
    ${REF_SHELLS[@]} $OSH "$@"
 }

diff --git a/test/wild.sh b/test/wild.sh
@@ -561,6 +561,10 @@ parse-bash-snippets() {
 }

 # ASDF meta package/version manager.
+# Note that the language-specific plugins are specified (as remote repos) here:
+# https://github.com/asdf-vm/asdf-plugins/tree/master/plugins
+# They could be used for more tests.
+
 parse-asdf() {
  local src=~/git/other/asdf