new file mode 100644
--- /dev/null
+++ b/src/json_test.c
@@ -0,0 +1,193 @@
+/* vi:set ts=8 sts=4 sw=4:
+ *
+ * VIM - Vi IMproved	by Bram Moolenaar
+ *
+ * Do ":help uganda"  in Vim to read copying and usage conditions.
+ * Do ":help credits" in Vim to see a list of people who contributed.
+ * See README.txt for an overview of the Vim source code.
+ */
+
+/*
+ * json_test.c: Unittests for json.c
+ */
+
+#undef NDEBUG
+#include <assert.h>
+
+/* Must include main.c because it contains much more than just main() */
+#define NO_VIM_MAIN
+#include "main.c"
+
+/* This file has to be included because the tested functions are static */
+#include "json.c"
+
+/*
+ * Test json_find_end() with imcomplete items.
+ */
+    static void
+test_decode_find_end(void)
+{
+    js_read_T reader;
+
+    reader.js_fill = NULL;
+    reader.js_used = 0;
+
+    /* string and incomplete string */
+    reader.js_buf = (char_u *)"\"hello\"";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"  \"hello\" ";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"\"hello";
+    assert(json_find_end(&reader) == MAYBE);
+
+    /* number and dash (incomplete number) */
+    reader.js_buf = (char_u *)"123";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"-";
+    assert(json_find_end(&reader) == MAYBE);
+
+    /* false, true and null, also incomplete */
+    reader.js_buf = (char_u *)"false";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"f";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"fa";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"fal";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"fals";
+    assert(json_find_end(&reader) == MAYBE);
+
+    reader.js_buf = (char_u *)"true";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"t";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"tr";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"tru";
+    assert(json_find_end(&reader) == MAYBE);
+
+    reader.js_buf = (char_u *)"null";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"n";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"nu";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"nul";
+    assert(json_find_end(&reader) == MAYBE);
+
+    /* object without white space */
+    reader.js_buf = (char_u *)"{\"a\":123}";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"{\"a\":123";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"{\"a\":";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"{\"a\"";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"{\"a";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"{\"";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"{";
+    assert(json_find_end(&reader) == MAYBE);
+
+    /* object with white space */
+    reader.js_buf = (char_u *)"  {  \"a\"  :  123  }  ";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"  {  \"a\"  :  123  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  {  \"a\"  :  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  {  \"a\"  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  {  \"a  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  {   ";
+    assert(json_find_end(&reader) == MAYBE);
+
+    /* array without white space */
+    reader.js_buf = (char_u *)"[\"a\",123]";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"[\"a\",123";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"[\"a\",";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"[\"a\"";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"[\"a";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"[\"";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"[";
+    assert(json_find_end(&reader) == MAYBE);
+
+    /* array with white space */
+    reader.js_buf = (char_u *)"  [  \"a\"  ,  123  ]  ";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"  [  \"a\"  ,  123  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  [  \"a\"  ,  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  [  \"a\"  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  [  \"a  ";
+    assert(json_find_end(&reader) == MAYBE);
+    reader.js_buf = (char_u *)"  [  ";
+    assert(json_find_end(&reader) == MAYBE);
+}
+
+    static int
+fill_from_cookie(js_read_T *reader)
+{
+    reader->js_buf = reader->js_cookie;
+    return TRUE;
+}
+
+/*
+ * Test json_find_end with an incomplete array, calling the fill function.
+ */
+    static void
+test_fill_called_on_find_end(void)
+{
+    js_read_T reader;
+
+    reader.js_fill = fill_from_cookie;
+    reader.js_used = 0;
+    reader.js_buf = (char_u *)"  [  \"a\"  ,  123  ";
+    reader.js_cookie =        "  [  \"a\"  ,  123  ]  ";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"  [  \"a\"  ,  ";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"  [  \"a\"  ";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"  [  \"a";
+    assert(json_find_end(&reader) == OK);
+    reader.js_buf = (char_u *)"  [  ";
+    assert(json_find_end(&reader) == OK);
+}
+
+/*
+ * Test json_find_end with an incomplete string, calling the fill function.
+ */
+    static void
+test_fill_called_on_string(void)
+{
+    js_read_T reader;
+
+    reader.js_fill = fill_from_cookie;
+    reader.js_used = 0;
+    reader.js_buf = (char_u *)" \"foo";
+    reader.js_end = reader.js_buf + STRLEN(reader.js_buf);
+    reader.js_cookie =        " \"foobar\"  ";
+    assert(json_decode_string(&reader, NULL) == OK);
+}
+
+    int
+main(void)
+{
+    test_decode_find_end();
+    test_fill_called_on_find_end();
+    test_fill_called_on_string();
+    return 0;
+}