Document (and fix) args format and variable expansion.

2 files changed, 5 insertions, 1 deletions

diff --git a/README b/README
index 6411733..7ab533e 100644
--- a/README
+++ b/README
@@ -13,6 +13,7 @@ standard output.
 Each test case consists of:
 
 * a set of command line arguments, not including the command name (`foo.args`)
+  - each argument is on its own line
 * the file fed to standard input (`foo.stdin`)
 * the expected output to the standard output (`foo.stdout`)
 * the expected output to the standard error (`foo.stderr`)
@@ -60,4 +61,7 @@ The shell scripts may use the following environment variables:
 
 * `DATADIR`: a temporary directory where files may be created by the test
 
+In addition, the `foo.args` files can use Pythonic string expansion:
+
+* `%(datadir)s` for the same value as `$DATADIR`
 
diff --git a/cmdtest b/cmdtest
index c7e616e..b4d797a 100755
--- a/cmdtest
+++ b/cmdtest
@@ -147,7 +147,7 @@ class CommandTester(cliapp.Application):
 
     def expand(self, strings):
         variables = {
-            'tempdir': self.tempdir,
+            'datadir': self.datadir,
         }
         return [s % variables for s in strings]