test: add unit tests for IO (link, fileInfo, chmod, permissions)

10 tests covering link creation, hardlink count, inode detection,
chmod permissions, FileNotFoundException on missing paths, and
permission constant values.

setStdoutStderrTo() is excluded from unit tests because dup2()
redirects the JVM's stdout/stderr, breaking surefire communication.

Refs: CO-3493

Author: M0Rf30

store/src/test/java/com/zimbra/znative/IOTest.java

@@ -0,0 +1,144 @@
+// SPDX-FileCopyrightText: 2025 Zextras <https://www.zextras.com>
+//
+// SPDX-License-Identifier: GPL-2.0-only
+
+package com.zimbra.znative;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.attribute.PosixFilePermission;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+class IOTest {
+
+  @TempDir Path tempDir;
+
+  @Test
+  void link_createsHardLink() throws IOException {
+    Path src = tempDir.resolve("source.txt");
+    Files.writeString(src, "hello");
+
+    String destPath = tempDir.resolve("dest.txt").toString();
+    IO.link(src.toString(), destPath);
+
+    assertEquals("hello", Files.readString(Path.of(destPath)));
+    // Hard link means same inode
+    assertEquals(
+        Files.getAttribute(src, "unix:ino"),
+        Files.getAttribute(Path.of(destPath), "unix:ino"));
+  }
+
+  @Test
+  void link_throwsFileNotFoundForMissingSrc() {
+    String missing = tempDir.resolve("nonexistent").toString();
+    String dest = tempDir.resolve("dest").toString();
+
+    assertThrows(FileNotFoundException.class, () -> IO.link(missing, dest));
+  }
+
+  @Test
+  void link_throwsIOExceptionForExistingDest() throws IOException {
+    Path src = tempDir.resolve("src.txt");
+    Path dest = tempDir.resolve("dest.txt");
+    Files.writeString(src, "a");
+    Files.writeString(dest, "b");
+
+    assertThrows(IOException.class, () -> IO.link(src.toString(), dest.toString()));
+  }
+
+  @Test
+  void fileInfo_returnsInodeSizeAndLinkCount() throws IOException {
+    Path file = tempDir.resolve("test.txt");
+    Files.writeString(file, "content");
+
+    IO.FileInfo info = IO.fileInfo(file.toString());
+
+    assertNotNull(info);
+    assertTrue(info.getInodeNum() > 0);
+    assertEquals(7, info.getSize()); // "content" is 7 bytes
+    assertEquals(1, info.getLinkCount());
+  }
+
+  @Test
+  void fileInfo_linkCountIncreasesAfterHardLink() throws IOException {
+    Path file = tempDir.resolve("original.txt");
+    Files.writeString(file, "data");
+
+    IO.FileInfo before = IO.fileInfo(file.toString());
+    assertEquals(1, before.getLinkCount());
+
+    IO.link(file.toString(), tempDir.resolve("linked.txt").toString());
+
+    IO.FileInfo after = IO.fileInfo(file.toString());
+    assertEquals(2, after.getLinkCount());
+    assertEquals(before.getInodeNum(), after.getInodeNum());
+  }
+
+  @Test
+  void fileInfo_throwsFileNotFoundForMissingPath() {
+    String missing = tempDir.resolve("nonexistent").toString();
+    assertThrows(FileNotFoundException.class, () -> IO.fileInfo(missing));
+  }
+
+  @Test
+  void linkCount_returnsCorrectCount() throws IOException {
+    Path file = tempDir.resolve("file.txt");
+    Files.writeString(file, "x");
+
+    assertEquals(1, IO.linkCount(file.toString()));
+
+    IO.link(file.toString(), tempDir.resolve("link1.txt").toString());
+    assertEquals(2, IO.linkCount(file.toString()));
+
+    IO.link(file.toString(), tempDir.resolve("link2.txt").toString());
+    assertEquals(3, IO.linkCount(file.toString()));
+  }
+
+  @Test
+  void chmod_setsPermissions() throws IOException {
+    Path file = tempDir.resolve("perms.txt");
+    Files.writeString(file, "test");
+
+    IO.chmod(file.toString(), IO.S_IRUSR | IO.S_IWUSR);
+
+    var perms = Files.getPosixFilePermissions(file);
+    assertTrue(perms.contains(PosixFilePermission.OWNER_READ));
+    assertTrue(perms.contains(PosixFilePermission.OWNER_WRITE));
+    assertFalse(perms.contains(PosixFilePermission.OWNER_EXECUTE));
+    assertFalse(perms.contains(PosixFilePermission.GROUP_READ));
+    assertFalse(perms.contains(PosixFilePermission.OTHERS_READ));
+  }
+
+  @Test
+  void chmod_throwsFileNotFoundForMissingPath() {
+    String missing = tempDir.resolve("nonexistent").toString();
+    assertThrows(FileNotFoundException.class, () -> IO.chmod(missing, IO.S_IRUSR));
+  }
+
+  // setStdoutStderrTo() tests are intentionally excluded:
+  // dup2() redirects stdout/stderr for the entire JVM process, which breaks
+  // surefire's communication pipe and causes "forked VM terminated" errors.
+  // This function is only used by MailboxServer output rotation and is tested
+  // in production via systemd service startup.
+
+  @Test
+  void permissionConstants_haveCorrectValues() {
+    assertEquals(0400, IO.S_IRUSR);
+    assertEquals(0200, IO.S_IWUSR);
+    assertEquals(0100, IO.S_IXUSR);
+    assertEquals(0040, IO.S_IRGRP);
+    assertEquals(0020, IO.S_IWGRP);
+    assertEquals(0010, IO.S_IXGRP);
+    assertEquals(0004, IO.S_IROTH);
+    assertEquals(0002, IO.S_IWOTH);
+    assertEquals(0001, IO.S_IXOTH);
+    assertEquals(04000, IO.S_ISUID);
+    assertEquals(02000, IO.S_ISGID);
+    assertEquals(01000, IO.S_ISVTX);
+  }
+}