test: Add new strnstr() unit test

test/.gitignore

@@ -18,3 +18,4 @@ progname
 setmode
 strl
 strmode
+strnstr

test/Makefile.am

@@ -46,6 +46,7 @@ check_PROGRAMS = \
 	setmode \
 	strl \
 	strmode \
+	strnstr \
 	$(nil)
 
 if HAVE_LIBTESTU01

test/strnstr.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright © 2017 Guillem Jover <guillem@hadrons.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
+ * THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <assert.h>
+#include <string.h>
+
+int
+main(int argc, char **argv)
+{
+	const char *large = "foo bar baz";
+	const char *small = "bar";
+
+	assert(strnstr(large, "", strlen(large)) == large);
+
+	assert(strnstr(large, "quux", strlen(large)) == NULL);
+
+	assert(strnstr(large, small, 4) == NULL);
+
+	assert(strnstr(large, small, strlen(large)) == (large + 4));
+
+	return 0;
+}