Use .zeek file suffix in unit tests

testing/btest/scripts/base/frameworks/logging/field-extension-complex.zeek

@@ -0,0 +1,37 @@
+# @TEST-EXEC: bro -b -r $TRACES/wikipedia.trace %INPUT
+# @TEST-EXEC: btest-diff conn.log
+
+@load base/protocols/conn
+
+type InnerRecord: record {
+	a: count;
+	b: count;
+	c: count;
+};
+
+type InnerLoggedRecord: record {
+	a: count &log;
+	b: count;
+	c: count &log;
+	d: set[count] &log;
+};
+
+type Extension: record {
+	write_ts: time &log;
+	stream: string &log;
+	inner: InnerRecord;
+	innerLogged: InnerLoggedRecord &log;
+	system_name: string &log;
+};
+
+function add_extension(path: string): Extension
+	{
+	return Extension($write_ts    = network_time(),
+	                 $stream      = path,
+	                 $system_name = peer_description,
+	                 $inner = InnerRecord($a=1,$b=2,$c=3),
+	                 $innerLogged = InnerLoggedRecord($a=1,$b=2,$c=3,$d=set(1,2,3,4))
+	                 );
+	}
+
+redef Log::default_ext_func = add_extension;