test(mknb): pin which program compresses the genesis image

Add a unit test for the routine that chooses the compression program. The
test lifts the routine out of the plugin source, because the plugin needs a
management node to load.

The test shows that lzma is used when it is there, that xz stands in when it
is not, and that xz is asked for the lzma container rather than its own. It
also shows that the caller takes the command from the routine, that the file
keeps its name and its suffix, and that the gzip fallback and the rename into
place both remain.

xCAT-test/unit/mknb_genesis_compressor.t

@@ -0,0 +1,54 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+
+use FindBin;
+use File::Spec;
+use Test::More;
+
+my $plugin = File::Spec->catfile( $FindBin::Bin, '..', '..',
+    'xCAT-server', 'lib', 'xcat', 'plugins', 'mknb.pm' );
+plan skip_all => 'mknb.pm not found' unless -r $plugin;
+
+open( my $fh, '<', $plugin ) or die "Unable to read $plugin: $!";
+my $source = do { local $/; <$fh> };
+close($fh);
+
+# mknb.pm needs a management node to load, so lift the routine out and drive
+# the real code on its own.
+my ($routine) = $source =~ /(sub genesis_lzma_command \{.*?\n\}\n)/s;
+BAIL_OUT('could not extract genesis_lzma_command from mknb.pm') unless $routine;
+eval "package MknbCompressor; $routine 1;" or BAIL_OUT("could not evaluate: $@");
+
+sub command { return MknbCompressor::genesis_lzma_command(@_); }
+
+# Debian and Ubuntu ship both names, and lzma is the one the plugin has always
+# used, so nothing changes on those systems.
+is( command( 1, 1 ), 'lzma -C crc32 -9', 'lzma is used when it is there' );
+
+# Red Hat ships xz alone.
+is( command( 0, 1 ), 'xz --format=lzma -C crc32 -9',
+    'xz stands in for lzma when only xz is there' );
+
+# The gzip path below the caller handles a system with neither.
+is( command( 0, 0 ), undef, 'nothing is returned when neither program is there' );
+
+# The container has to stay the one the file name promises. "xz" on its own
+# writes the xz container, which the file name does not describe and which a
+# reader of a .lzma file cannot open.
+my ($xz_form) = command( 0, 1 ) =~ /--format=(\S+)/;
+is( $xz_form, 'lzma', 'xz is asked for the lzma container, not its own' );
+
+# The caller has to take the command from the routine, and the name of the
+# written file must not change with it.
+like( $source, qr/genesis_lzma_command\(-x "\/usr\/bin\/lzma", -x "\/usr\/bin\/xz"\)/,
+    'the caller asks the routine which program to run' );
+like( $source, qr/cpio -o -H newc \| \$lzma_command > \$tftpdir\/xcat\/genesis\.fs\.\$arch\.lzma\.\$suffix/,
+    'the chosen command writes the same file under the same suffix' );
+
+# The fallback to gzip and the atomic rename both have to survive.
+like( $source, qr/falling back to gzip/, 'the gzip fallback is still reported' );
+like( $source, qr/move\("\$tftpdir\/xcat\/genesis\.fs\.\$arch\.lzma\.\$suffix"/,
+    'the finished image is still renamed into place' );
+
+done_testing();