increasing test coverage

Signed-off-by: Pradeep L <spradeel@amazon.com>

Author: Pradeep L

server/src/main/java/org/opensearch/monitor/os/OsProbe.java

@@ -39,7 +39,6 @@
 import org.opensearch.common.io.PathUtils;
 import org.opensearch.monitor.Probes;
 
-import java.io.BufferedReader;
 import java.io.IOException;
 import java.lang.management.ManagementFactory;
 import java.lang.management.OperatingSystemMXBean;
@@ -259,40 +258,47 @@ public long getProcessRssAnon() {
     }
 
     /**
-     * Reads the {@code RssAnon} field from {@code /proc/self/status}. Package-private so tests
-     * can override it with canned file contents.
+     * Reads the lines of {@code /proc/self/status}. Package-private so tests can override it
+     * with canned file contents.
+     *
+     * @return the lines of {@code /proc/self/status}
+     * @throws IOException if the file cannot be opened or read
+     */
+    @SuppressForbidden(reason = "access /proc/self/status")
+    List<String> readProcSelfStatus() throws IOException {
+        return Files.readAllLines(PathUtils.get("/proc/self/status"));
+    }
+
+    /**
+     * Reads the {@code RssAnon} field from {@code /proc/self/status}.
      *
      * @return the {@code RssAnon} value in bytes, or {@code -1L} when the line is missing or
      *         the value is unparseable/negative
      * @throws IOException if the file cannot be opened or read
      */
-    @SuppressForbidden(reason = "access /proc/self/status")
     long readRssAnonFromProcSelfStatus() throws IOException {
-        try (BufferedReader reader = Files.newBufferedReader(PathUtils.get("/proc/self/status"))) {
-            String line;
-            while ((line = reader.readLine()) != null) {
-                if (line.startsWith("RssAnon:")) {
-                    // Format: "RssAnon:\t 12345 kB"
-                    String[] parts = line.split("\\s+");
-                    if (parts.length >= 2) {
-                        try {
-                            long kb = Long.parseLong(parts[1]);
-                            if (kb < 0L) {
-                                return -1L;
-                            }
-                            return kb * 1024L;
-                        } catch (NumberFormatException nfe) {
-                            logger.warn("malformed RssAnon value in /proc/self/status", nfe);
+        for (final String line : readProcSelfStatus()) {
+            if (line.startsWith("RssAnon:")) {
+                // Format: "RssAnon:\t 12345 kB"
+                final String[] parts = line.split("\\s+");
+                if (parts.length >= 2) {
+                    try {
+                        final long kb = Long.parseLong(parts[1]);
+                        if (kb < 0L) {
                             return -1L;
                         }
+                        return kb * 1024L;
+                    } catch (NumberFormatException nfe) {
+                        logger.warn("malformed RssAnon value in /proc/self/status", nfe);
+                        return -1L;
                     }
-                    logger.warn("RssAnon line has unexpected shape: [{}]", line);
-                    return -1L;
                 }
+                logger.warn("RssAnon line has unexpected shape: [{}]", line);
+                return -1L;
             }
-            logger.warn("RssAnon line not found in /proc/self/status");
-            return -1L;
         }
+        logger.warn("RssAnon line not found in /proc/self/status");
+        return -1L;
     }
 
     public short getSystemCpuPercent() {

server/src/test/java/org/opensearch/monitor/os/OsProbeTests.java

@@ -56,7 +56,9 @@
 import static org.hamcrest.Matchers.lessThanOrEqualTo;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.junit.Assume.assumeThat;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.reset;
@@ -310,6 +312,120 @@ List<String> readSysFsCgroupCpuAcctCpuStat(String controlGroup) throws IOExcepti
         verify(logger, never()).warn(anyString());
     }
 
+    public void testGetProcessRssAnonNotLinuxReturnsNegativeOne() {
+        assumeFalse("test runs on non-Linux only", Constants.LINUX);
+        final OsProbe probe = new OsProbe() {
+            @Override
+            List<String> readProcSelfStatus() {
+                throw new AssertionError("readProcSelfStatus should not be called on non-Linux");
+            }
+        };
+        assertThat(probe.getProcessRssAnon(), equalTo(-1L));
+    }
+
+    public void testGetProcessRssAnonReturnsBytes() {
+        assumeTrue("test runs on Linux only", Constants.LINUX);
+        final OsProbe probe = new OsProbe() {
+            @Override
+            List<String> readProcSelfStatus() {
+                return Arrays.asList("Name:\topensearch", "VmRSS:\t  98304 kB", "RssAnon:\t  4096 kB", "RssFile:\t  2048 kB");
+            }
+        };
+        assertThat(probe.getProcessRssAnon(), equalTo(4096L * 1024L));
+    }
+
+    public void testGetProcessRssAnonHandlesIOException() {
+        assumeTrue("test runs on Linux only", Constants.LINUX);
+        final Logger logger = mock(Logger.class);
+        final OsProbe probe = new OsProbe(logger) {
+            @Override
+            List<String> readProcSelfStatus() throws IOException {
+                throw new IOException("simulated failure");
+            }
+        };
+        assertThat(probe.getProcessRssAnon(), equalTo(-1L));
+        verify(logger, times(1)).warn(eq("failed to read /proc/self/status"), any(IOException.class));
+    }
+
+    public void testReadRssAnonFromProcSelfStatusValidValue() throws IOException {
+        final OsProbe probe = new OsProbe() {
+            @Override
+            List<String> readProcSelfStatus() {
+                return Arrays.asList("Name:\topensearch", "VmPeak:\t  131072 kB", "RssAnon:\t  12345 kB", "RssShmem:\t  64 kB");
+            }
+        };
+        assertThat(probe.readRssAnonFromProcSelfStatus(), equalTo(12345L * 1024L));
+    }
+
+    public void testReadRssAnonFromProcSelfStatusZeroValue() throws IOException {
+        final OsProbe probe = new OsProbe() {
+            @Override
+            List<String> readProcSelfStatus() {
+                return Collections.singletonList("RssAnon:\t  0 kB");
+            }
+        };
+        assertThat(probe.readRssAnonFromProcSelfStatus(), equalTo(0L));
+    }
+
+    public void testReadRssAnonFromProcSelfStatusNegativeValue() throws IOException {
+        final OsProbe probe = new OsProbe() {
+            @Override
+            List<String> readProcSelfStatus() {
+                return Collections.singletonList("RssAnon:\t  -1 kB");
+            }
+        };
+        assertThat(probe.readRssAnonFromProcSelfStatus(), equalTo(-1L));
+    }
+
+    public void testReadRssAnonFromProcSelfStatusMalformedValue() throws IOException {
+        final Logger logger = mock(Logger.class);
+        final OsProbe probe = new OsProbe(logger) {
+            @Override
+            List<String> readProcSelfStatus() {
+                return Collections.singletonList("RssAnon:\tnotanumber kB");
+            }
+        };
+        assertThat(probe.readRssAnonFromProcSelfStatus(), equalTo(-1L));
+        verify(logger, times(1)).warn(eq("malformed RssAnon value in /proc/self/status"), any(NumberFormatException.class));
+    }
+
+    public void testReadRssAnonFromProcSelfStatusUnexpectedShape() throws IOException {
+        final Logger logger = mock(Logger.class);
+        final OsProbe probe = new OsProbe(logger) {
+            @Override
+            List<String> readProcSelfStatus() {
+                // No whitespace after the label, so split produces a single token
+                return Collections.singletonList("RssAnon:");
+            }
+        };
+        assertThat(probe.readRssAnonFromProcSelfStatus(), equalTo(-1L));
+        verify(logger, times(1)).warn("RssAnon line has unexpected shape: [{}]", "RssAnon:");
+    }
+
+    public void testReadRssAnonFromProcSelfStatusMissingLine() throws IOException {
+        final Logger logger = mock(Logger.class);
+        final OsProbe probe = new OsProbe(logger) {
+            @Override
+            List<String> readProcSelfStatus() {
+                return Arrays.asList("Name:\topensearch", "VmRSS:\t  98304 kB");
+            }
+        };
+        assertThat(probe.readRssAnonFromProcSelfStatus(), equalTo(-1L));
+        verify(logger, times(1)).warn("RssAnon line not found in /proc/self/status");
+    }
+
+    public void testReadRssAnonFromProcSelfStatusEmptyFile() throws IOException {
+        final Logger logger = mock(Logger.class);
+        final OsProbe probe = new OsProbe(logger) {
+            @Override
+            List<String> readProcSelfStatus() {
+                return Collections.emptyList();
+            }
+        };
+        assertThat(probe.readRssAnonFromProcSelfStatus(), equalTo(-1L));
+        verify(logger, times(1)).warn("RssAnon line not found in /proc/self/status");
+    }
+
     private static List<String> getProcSelfGroupLines(String hierarchy) {
         return Arrays.asList(
             "10:freezer:/",