add mimimal tests

t/assets/hello.txt

@@ -0,0 +1 @@
+hello

t/blockdiff_dump.t

@@ -0,0 +1,59 @@
+use strict;
+use warnings;
+
+use Digest::MD5 qw(md5);
+use File::Temp qw(tempdir);
+use POSIX qw(:sys_wait_h);
+use Test::More;
+
+my $BS_HDR = "\0\x40\0\0"; # 16384 (block size) in little endian
+
+my $tempdir = tempdir(CLEANUP => 1);
+
+# full backup test
+my $out = runit("t/assets/hello.txt");
+my $status = $?;
+ok WIFEXITED($?), 'blockdiff_dump exited';
+is WEXITSTATUS($?), 0, 'blockdiff_dump exit code';
+is(
+    $out,
+    $BS_HDR . ("\0"x8) . read_file('t/assets/hello.txt'),
+    'blockdiff_dump output',
+);
+is(
+    read_file("$tempdir/md5.out"),
+    $BS_HDR . md5(read_file('t/assets/hello.txt')),
+    'blockdiff_dump md5 output',
+);
+
+# nexist
+runit("t/assets/nexist.txt", 1);
+$status = $?;
+ok WIFEXITED($?), 'blockdiff_dump exitted';
+isnt WEXITSTATUS($?), 0, 'blockdiff_dump error on exit';
+
+# TODO: incremental backup
+
+# TODO: -z and --lzop
+
+done_testing;
+
+sub runit {
+    my ($fn, $no_stderr) = @_;
+    open(
+        my $fh,
+        '-|',
+        "blib/script/blockdiff_dump $fn 6> $tempdir/md5.out"
+            . ($no_stderr ? ' 2> /dev/null' : ''),
+    ) or die "failed to exec blockdiff:$!";
+    my $out = join '', <$fh>;
+    close $fh;
+    $out;
+}
+
+sub read_file {
+    my $fn = shift;
+    open my $fh, '<', $fn
+        or die "failed to open file:$fn:$!";
+    return join '', <$fh>;
+}