More improvements to submodule diff tests

This controls for the diff.mnemonicprefix setting so that can't
break the tests.  Also, this expands one test to emulate an
ObjectiveGit test more closely.

tests-clar/diff/submodules.c

@@ -86,6 +86,7 @@ void test_diff_submodules__unmodified_submodule(void)
 	opts.flags = GIT_DIFF_INCLUDE_IGNORED |
 		GIT_DIFF_INCLUDE_UNTRACKED |
 		GIT_DIFF_INCLUDE_UNMODIFIED;
+	opts.old_prefix = "a"; opts.new_prefix = "b";
 
 	cl_git_pass(git_diff_index_to_workdir(&diff, g_repo, NULL, &opts));
 	check_diff_patches(diff, expected);
@@ -115,6 +116,7 @@ void test_diff_submodules__dirty_submodule(void)
 	opts.flags = GIT_DIFF_INCLUDE_IGNORED |
 		GIT_DIFF_INCLUDE_UNTRACKED |
 		GIT_DIFF_INCLUDE_UNMODIFIED;
+	opts.old_prefix = "a"; opts.new_prefix = "b";
 
 	cl_git_pass(git_diff_index_to_workdir(&diff, g_repo, NULL, &opts));
 	check_diff_patches(diff, expected);
@@ -124,9 +126,9 @@ void test_diff_submodules__dirty_submodule(void)
 void test_diff_submodules__dirty_submodule_2(void)
 {
 	git_diff_options opts = GIT_DIFF_OPTIONS_INIT;
-	git_diff_list *diff = NULL;
+	git_diff_list *diff = NULL, *diff2 = NULL;
 	char *smpath = "testrepo";
-	static const char *expected_none[] = { NULL, "<END>" };
+	static const char *expected_none[] = { "<END>" };
 	static const char *expected_dirty[] = {
 		"diff --git a/testrepo b/testrepo\nindex a65fedf..a65fedf 160000\n--- a/testrepo\n+++ b/testrepo\n@@ -1 +1 @@\n-Subproject commit a65fedf39aefe402d3bb6e24df4d4f5fe4547750\n+Subproject commit a65fedf39aefe402d3bb6e24df4d4f5fe4547750-dirty\n", /* testrepo.git */
 		"<END>"
@@ -136,9 +138,11 @@ void test_diff_submodules__dirty_submodule_2(void)
 
 	cl_git_pass(git_submodule_reload_all(g_repo));
 
-	opts.flags = GIT_DIFF_INCLUDE_IGNORED |
-		GIT_DIFF_INCLUDE_UNTRACKED |
-		GIT_DIFF_INCLUDE_UNMODIFIED;
+	opts.flags = GIT_DIFF_INCLUDE_UNTRACKED |
+		GIT_DIFF_INCLUDE_UNTRACKED_CONTENT |
+		GIT_DIFF_RECURSE_UNTRACKED_DIRS |
+		GIT_DIFF_DISABLE_PATHSPEC_MATCH;
+	opts.old_prefix = "a"; opts.new_prefix = "b";
 	opts.pathspec.count = 1;
 	opts.pathspec.strings = &smpath;
 
@@ -151,6 +155,18 @@ void test_diff_submodules__dirty_submodule_2(void)
 
 	cl_git_pass(git_diff_index_to_workdir(&diff, g_repo, NULL, &opts));
 	check_diff_patches(diff, expected_dirty);
+
+	{
+		git_tree *head;
+
+		cl_git_pass(git_repository_head_tree(&head, g_repo));
+		cl_git_pass(git_diff_tree_to_index(&diff2, g_repo, head, NULL, &opts));
+		cl_git_pass(git_diff_merge(diff, diff2));
+		git_diff_list_free(diff2);
+
+		check_diff_patches(diff, expected_dirty);
+	}
+
 	git_diff_list_free(diff);
 
 	cl_git_pass(git_submodule_reload_all(g_repo));
@@ -179,6 +195,7 @@ void test_diff_submodules__submod2_index_to_wd(void)
 	setup_submodules2();
 
 	opts.flags = GIT_DIFF_INCLUDE_UNTRACKED;
+	opts.old_prefix = "a"; opts.new_prefix = "b";
 
 	cl_git_pass(git_diff_index_to_workdir(&diff, g_repo, NULL, &opts));
 	check_diff_patches(diff, expected);
@@ -201,6 +218,7 @@ void test_diff_submodules__submod2_head_to_index(void)
 	cl_git_pass(git_repository_head_tree(&head, g_repo));
 
 	opts.flags = GIT_DIFF_INCLUDE_UNTRACKED;
+	opts.old_prefix = "a"; opts.new_prefix = "b";
 
 	cl_git_pass(git_diff_tree_to_index(&diff, g_repo, head, NULL, &opts));
 	check_diff_patches(diff, expected);