patch 8.0.1048: no test for what 8.0.1020 fixes

Problem:    No test for what 8.0.1020 fixes.
Solution:   Add test_feedinput().  Add a test. (Ozaki Kiichi, closes #2046)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 626af7c..2692de6 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -393,6 +393,7 @@
 static void f_tempname(typval_T *argvars, typval_T *rettv);
 static void f_test_alloc_fail(typval_T *argvars, typval_T *rettv);
 static void f_test_autochdir(typval_T *argvars, typval_T *rettv);
+static void f_test_feedinput(typval_T *argvars, typval_T *rettv);
 static void f_test_override(typval_T *argvars, typval_T *rettv);
 static void f_test_garbagecollect_now(typval_T *argvars, typval_T *rettv);
 static void f_test_ignore_error(typval_T *argvars, typval_T *rettv);
@@ -851,6 +852,7 @@
 #endif
     {"test_alloc_fail",	3, 3, f_test_alloc_fail},
     {"test_autochdir",	0, 0, f_test_autochdir},
+    {"test_feedinput",	1, 1, f_test_feedinput},
     {"test_garbagecollect_now",	0, 0, f_test_garbagecollect_now},
     {"test_ignore_error",	1, 1, f_test_ignore_error},
 #ifdef FEAT_JOB_CHANNEL
@@ -12518,6 +12520,23 @@
 }
 
 /*
+ * "test_feedinput()"
+ */
+    static void
+f_test_feedinput(typval_T *argvars, typval_T *rettv UNUSED)
+{
+#ifdef USE_INPUT_BUF
+    char_u	*val = get_tv_string_chk(&argvars[0]);
+
+    if (val != NULL)
+    {
+	trash_input_buf();
+	add_to_input_buf_csi(val, (int)STRLEN(val));
+    }
+#endif
+}
+
+/*
  * "test_disable({name}, {val})" function
  */
     static void