Pass a test file to flex test.

diff --git a/test cases/frameworks/8 flex/meson.build b/test cases/frameworks/8 flex/meson.build
index cb5efde..bc84bcc 100644
--- a/test cases/frameworks/8 flex/meson.build
+++ b/test cases/frameworks/8 flex/meson.build

@@ -30,4 +30,5 @@
 e = executable('pgen', 'prog.c',
 lfiles, pfiles)
 
-test('parsertest', e)
+test('parsertest', e,
+    args: [meson.current_source_dir() / 'testfile'])

diff --git a/test cases/frameworks/8 flex/prog.c b/test cases/frameworks/8 flex/prog.c
index d94d7b1..ae481d0 100644
--- a/test cases/frameworks/8 flex/prog.c
+++ b/test cases/frameworks/8 flex/prog.c

@@ -11,7 +11,7 @@
 int main(int argc, char **argv) {
     int input;
     if(argc != 2) {
-        printf("%s <input file>");
+        printf("%s <input file>\n", argv[0]);
         return 1;
     }
     input = open(argv[1], O_RDONLY);

diff --git a/test cases/frameworks/8 flex/testfile b/test cases/frameworks/8 flex/testfile
new file mode 100644
index 0000000..7eead1e
--- /dev/null
+++ b/test cases/frameworks/8 flex/testfile

@@ -0,0 +1,2 @@
+true
+