Try to use /usr/bin/test or /bin/test to work around missing features.
The builtin "test" of Solaris 8 /bin/sh doesn't understand -nt.
#!/bin/sh
cat <<'EOF' > merge
#!/bin/sh
echo merging for `basename $1`
EOF
chmod +x merge
mkdir t
cd t
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
hg update 0
echo This is file c1 > c
hg add c
hg commit -m "commit #2" -d "1000000 0"
echo This is file b1 > b
echo %% no merges expected
env HGMERGE=../merge hg update -m 1
cd ..; /bin/rm -rf t
mkdir t
cd t
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
hg update 0
echo This is file c1 > c
hg add c
hg commit -m "commit #2" -d "1000000 0"
echo This is file b2 > b
echo %% merge should fail
env HGMERGE=../merge hg update -m 1
echo %% merge of b expected
env HGMERGE=../merge hg update -f -m 1
cd ..; /bin/rm -rf t
echo %%
mkdir t
cd t
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
echo This is file b22 > b
hg commit -m "commit #2" -d "1000000 0"
hg update 1
echo This is file c1 > c
hg add c
hg commit -m "commit #3" -d "1000000 0"
echo 'Contents of b should be "this is file b1"'
cat b
echo This is file b22 > b
echo %% merge fails
env HGMERGE=../merge hg update -m 2
echo %% merge expected!
env HGMERGE=../merge hg update -f -m 2
cd ..; /bin/rm -rf t
mkdir t
cd t
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
echo This is file b22 > b
hg commit -m "commit #2" -d "1000000 0"
hg update 1
echo This is file c1 > c
hg add c
hg commit -m "commit #3" -d "1000000 0"
echo This is file b33 > b
echo %% merge of b should fail
env HGMERGE=../merge hg update -m 2
echo %% merge of b expected
env HGMERGE=../merge hg update -f -m 2
cd ..; /bin/rm -rf t