test_common: add create_inbox helper sub

This saves over 100ms in t/lei-q-remote-import.t so far when
TMPDIR is on an SSD.  If we can memoize inbox creation to save a
few dozen milliseconds every test, this could add up to
noticeable savings across our entire test suite.

1 files changed, 2 insertions, 1 deletions

diff --git a/Makefile.PL b/Makefile.PL
index 21d3d6ea..8165e601 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -176,7 +176,8 @@ WriteMakefile(
         },
         MAN3PODS => \%man3,
         clean => {
-                FILES => 't/home*/setup* t/home*/t* t/home*/.public-inbox'
+                FILES => 't/home*/setup* t/home*/t* t/home*/.public-inbox '.
+                        't/data-gen/*'
         },
 );