patch/Tests: Add some initial tests for patch utility

Tests/Utilities/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(TEST_SOURCES
     TestSed.cpp
+    TestPatch.cpp
 )
 
 foreach(source IN LISTS TEST_SOURCES)

Tests/Utilities/TestPatch.cpp

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2023, Shannon Booth <shannon@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/StringView.h>
+#include <LibCore/Command.h>
+#include <LibCore/File.h>
+#include <LibCore/System.h>
+#include <LibFileSystem/FileSystem.h>
+#include <LibTest/Macros.h>
+#include <LibTest/TestCase.h>
+
+static constexpr char const* s_test_dir = "/tmp/patch-test";
+
+#define EXPECT_FILE_EQ(file_path, expected_content)                                  \
+    do {                                                                             \
+        auto output = MUST(Core::File::open(file_path, Core::File::OpenMode::Read)); \
+        auto content = MUST(output->read_until_eof());                               \
+        EXPECT_EQ(StringView { content }, expected_content);                         \
+    } while (false)
+
+class PatchSetup {
+public:
+    PatchSetup()
+    {
+        clean_up(); // Just in case something was left behind from beforehand.
+        MUST(Core::System::mkdir(StringView { s_test_dir, strlen(s_test_dir) }, 0755));
+    }
+
+    ~PatchSetup()
+    {
+        clean_up();
+    }
+
+private:
+    static void clean_up()
+    {
+        auto result = FileSystem::remove(StringView { s_test_dir, strlen(s_test_dir) }, FileSystem::RecursionMode::Allowed);
+        if (result.is_error())
+            VERIFY(result.error().is_errno() && result.error().code() == ENOENT);
+    }
+};
+
+static void run_patch(Vector<char const*>&& arguments, StringView standard_input, StringView expected_stdout)
+{
+    // Ask patch to run the test in a temporary directory so we don't leave any files around.
+    Vector<char const*> args_with_chdir = { "patch", "-d", s_test_dir };
+    args_with_chdir.extend(arguments);
+    args_with_chdir.append(nullptr);
+
+    auto patch = MUST(Core::Command::create("patch"sv, args_with_chdir.data()));
+
+    MUST(patch->write(standard_input));
+
+    auto [stdout, stderr] = MUST(patch->read_all());
+
+    auto status = MUST(patch->status());
+    if (status != Core::Command::ProcessResult::DoneWithZeroExitCode) {
+        FAIL(MUST(String::formatted("patch didn't exit cleanly: status: {}, stdout:{}, stderr: {}", static_cast<int>(status), StringView { stdout.bytes() }, StringView { stderr.bytes() })));
+    }
+    EXPECT_EQ(StringView { expected_stdout.bytes() }, StringView { stdout.bytes() });
+}
+
+TEST_CASE(basic_change_patch)
+{
+    PatchSetup setup;
+
+    auto patch = R"(
+--- a
++++ b
+@@ -1,3 +1,3 @@
+ 1
+-2
++b
+ 3
+)"sv;
+
+    auto file = "1\n2\n3\n"sv;
+    auto input = MUST(Core::File::open(MUST(String::formatted("{}/a", s_test_dir)), Core::File::OpenMode::Write));
+    MUST(input->write_until_depleted(file.bytes()));
+
+    run_patch({}, patch, "patching file a\n"sv);
+
+    EXPECT_FILE_EQ(MUST(String::formatted("{}/a", s_test_dir)), "1\nb\n3\n");
+}
+
+TEST_CASE(basic_addition_patch_from_empty_file)
+{
+    PatchSetup setup;
+
+    auto patch = R"(
+--- /dev/null
++++ a
+@@ -0,0 +1,3 @@
++1
++2
++3
+)"sv;
+
+    auto file = ""sv;
+    auto input = MUST(Core::File::open(MUST(String::formatted("{}/a", s_test_dir)), Core::File::OpenMode::Write));
+    MUST(input->write_until_depleted(file.bytes()));
+
+    run_patch({}, patch, "patching file a\n"sv);
+
+    EXPECT_FILE_EQ(MUST(String::formatted("{}/a", s_test_dir)), "1\n2\n3\n");
+}