I guess there are encoding differences that I cannot 'see'.

slurp.out

% make t/spec/S32-io/slurp.t
t/spec/S32-io/slurp.rakudo.jvm .. 
1..16
ok 1 - slurp() on non-existent files fails
ok 2 - slurp() on directories fails
ok 3 - test file slurp with path call ok
ok 4 - slurp returns a string
not ok 5 - slurp with path loads entire file
#      got: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
# expected: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
ok 6 - empty files yield empty string
not ok 7 - method form .slurp works
#      got: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
# expected: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
not ok 8 - function passed a filehandle works
#      got: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
# expected: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
not ok 9 - slurp with no parameters loads $*ARGFILES
#      got: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
# expected: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
ok 10 - # SKIP IO::Handle.read NYI on this backend
ok 11 - # SKIP IO::Handle.read NYI on this backend
ok 12 - # SKIP IO::Handle.read NYI on this backend
ok 13 - slurp :enc - encoding functions
not ok 14 - utf8 looks normal
#      got: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
# expected: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
not ok 15 - iso-8859-1 makes mojibake correctly
#      got: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
# expected: '0123456789
# ABCDEFG
# 風, 薔薇, バズ
# '
not ok 16 - lines() - exactly 3 lines in this file
#      got: '4'
# expected: '3'
# FUDGED!
# Looks like you failed 7 tests of 16
Failed 7/16 subtests 
  (less 3 skipped subtests: 6 okay)

Test Summary Report
-------------------
t/spec/S32-io/slurp.rakudo.jvm (Wstat: 0 Tests: 16 Failed: 7)
  Failed tests:  5, 7-9, 14-16
Files=1, Tests=16, 20 wallclock secs ( 0.03 usr  0.01 sys +  0.04 cusr  0.01 csys =  0.09 CPU)
Result: FAIL