tests: explicitly define compression engines for tests
The zstd compression engine requires C extensions and isn't present
in pure Python builds.
The compression engine list leaks into the server capabilities string.
Unless we're testing functionality specific to a compression format,
the set of compression formats supported by a server doesn't matter
much.
So this commit explicitly defines the server's compression engines for
some tests so behavior is consistent between pure and non-pure builds.
Differential Revision: https://phab.mercurial-scm.org/D3431
$ hg init
$ $PYTHON -c 'open("a", "wb").write(b"confuse str.splitlines\nembedded\rnewline\n")'
$ hg ci -Ama -d '1 0'
adding a
$ echo clean diff >> a
$ hg ci -mb -d '2 0'
$ hg diff -r0 -r1
diff -r 107ba6f817b5 -r 310ce7989cdc a
--- a/a Thu Jan 01 00:00:01 1970 +0000
+++ b/a Thu Jan 01 00:00:02 1970 +0000
@@ -1,2 +1,3 @@
confuse str.splitlines
embedded\r (no-eol) (esc)
newline
+clean diff