beef up write syscall tests

Added a few tests for write(2) and pwrite(2)

1. Regular Files

For write(2)

- write zero bytes should not move the offset
- write non-zero bytes should increment the offset the exact amount
- write non-zero bytes after a lseek() should move the offset the exact amount after the seek
- write non-zero bytes with O_APPEND should move the offset the exact amount after original EOF

For pwrite(2), offset is not affected when

- pwrite zero bytes
- pwrite non-zero bytes

For EOF, added a test asserting the EOF (indicated by lseek(SEEK_END)) is updated properly after writing non-zero bytes

2. Symlink

Added one pwite64() call for symlink that is written as a counterpart of the existing test using pread64()

0 files changed, 0 insertions, 0 deletions