Add missing android.system.Os test coverage.

Bug: 331618267
Test: CtsLibcoreTestCases:libcore.android.system.Os
Change-Id: If08297be3c7fe3614ffc6c8e408e59ed8dcf9af1

1 files changed, 55 insertions, 0 deletions

diff --git a/luni/src/test/java/libcore/android/system/OsTest.java b/luni/src/test/java/libcore/android/system/OsTest.java
index 90255c5f581..209f30bec27 100644
--- a/luni/src/test/java/libcore/android/system/OsTest.java
+++ b/luni/src/test/java/libcore/android/system/OsTest.java
@@ -53,6 +53,8 @@ import java.net.SocketException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
 import java.time.Duration;
 import java.util.Arrays;
 import java.util.Collections;
@@ -65,8 +67,12 @@ import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 import libcore.io.IoUtils;
 import libcore.testing.io.TestIoUtils;
+
+import org.junit.Assert;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -78,11 +84,14 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 import static org.junit.Assume.assumeNoException;
 import static org.junit.Assume.assumeTrue;
 
+import jdk.internal.misc.Unsafe;
+
 @RunWith(JUnit4.class)
 public class OsTest {
 
@@ -2251,6 +2260,52 @@ public class OsTest {
             "unsetenv(\"a=b\")");
     }
 
+    @Test
+    public void tcdrain_throwsWhenFdIsNotTty() throws Exception {
+        File temp = Files.createTempFile("regular-file", "txt").toFile();
+        FileDescriptor fd = Os.open(temp.getAbsolutePath(), O_RDWR, 0);
+
+        try {
+            assertThrows(ErrnoException.class, () -> Os.tcdrain(fd));
+        } finally {
+            if (fd != null) {
+                Os.close(fd);
+            }
+        }
+    }
+
+    @Test
+    public void testMsync() throws Exception {
+        File temp = Files.createTempFile("regular-file", "txt").toFile();
+
+        try (FileOutputStream fos = new FileOutputStream(temp)) {
+            fos.write("hello".getBytes(StandardCharsets.UTF_8));
+            fos.flush();
+        }
+
+        final long size = 5;
+        FileDescriptor fd = Os.open(temp.getAbsolutePath(), O_RDWR, 0);
+        final long address = Os.mmap(0, size, PROT_WRITE,
+                MAP_SHARED, fd, 0);
+        assertTrue(address > 0);
+
+        // The easiest way to write at address from Java I came up with.
+        var field = Unsafe.class.getDeclaredField("THE_ONE");
+        field.setAccessible(true);
+        Unsafe unsafe = (Unsafe) field.get(null);
+        unsafe.setMemory(address, size, (byte) 'a');
+
+        Os.msync(address, size, MS_SYNC);
+
+        try (Stream<String> stream = Files.lines(temp.toPath())) {
+            List<String> lines = stream.toList();
+            assertEquals(1, lines.size());
+            assertEquals("a".repeat((int) size), lines.get(0));
+        }
+
+        Os.munmap(address, size);
+    }
+
     /*
      * Checks that all ways of accessing the environment are consistent by collecting:
      * osEnvironment      - The environment returned by Os.environ()