fix: Fallback to existing evaluation context on failed refresh

src/main/java/com/octopus/openfeature/provider/OctopusContextProvider.java

@@ -52,7 +52,11 @@ void refresh() {
 
                 if (client.haveFeatureTogglesChanged(currentContext.getContentHash())) {
                     var toggles = client.getFeatureToggleEvaluationManifest();
-                    currentContext = toggles == null ? OctopusContext.empty() : new OctopusContext(toggles);
+                    if (toggles != null) {
+                        currentContext = new OctopusContext(toggles);
+                    } else {
+                        logger.log(System.Logger.Level.ERROR, "Failed to retrieve updated feature manifest. Retaining existing context which may be stale.");
+                    }
                 }
 
                 delay = config.getCacheDuration();

src/test/java/com/octopus/openfeature/provider/OctopusContextProviderTests.java

@@ -0,0 +1,124 @@
+package com.octopus.openfeature.provider;
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.logging.Handler;
+import java.util.logging.LogRecord;
+import java.util.logging.Logger;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.jupiter.api.Test;
+
+class OctopusContextProviderTests {
+
+    static class MockOctopusFeatureClient extends OctopusClient {
+
+        private volatile FeatureToggles toggles;
+
+        MockOctopusFeatureClient(FeatureToggles toggles) {
+            super(null);
+            this.toggles = toggles;
+        }
+
+        void changeToggles(FeatureToggles toggles) {
+            this.toggles = toggles;
+        }
+
+        @Override
+        Boolean haveFeatureTogglesChanged(byte[] contentHash) {
+            return true;
+        }
+
+        @Override
+        FeatureToggles getFeatureToggleEvaluationManifest() {
+            return toggles;
+        }
+    }
+
+    private final OctopusConfiguration configuration = configure();
+
+    private static OctopusConfiguration configure() {
+        var config = new OctopusConfiguration("token");
+        config.setCacheDuration(Duration.ofMillis(100));
+        return config;
+    }
+
+    @Test
+    void whenInitialized_RefreshesCacheAfterCacheDurationExpires() throws InterruptedException {
+
+        byte[] initialHash = {0x01, 0x02, 0x03, 0x04};
+        byte[] updatedHash = {0x01, 0x02, 0x03, 0x05};
+
+        var client = new MockOctopusFeatureClient(new FeatureToggles(
+            List.of(new FeatureToggleEvaluation("test-feature", true, "evaluation-key", Collections.emptyList(), 100)),
+            initialHash
+        ));
+
+        var provider = new OctopusContextProvider(configuration, client);
+        provider.initialize();
+
+        try {
+            // Validate the initial state
+            assertThat(provider.getOctopusContext().getContentHash()).isEqualTo(initialHash);
+            assertThat(provider.getOctopusContext().evaluate("test-feature", false, null).getValue()).isTrue();
+
+            // Simulate a change in the available feature toggles
+            client.changeToggles(new FeatureToggles(
+                List.of(new FeatureToggleEvaluation("test-feature", false, "evaluation-key", Collections.emptyList(), 100)),
+                updatedHash
+            ));
+
+            // Wait for the cache to expire
+            Thread.sleep(500);
+
+            // Validate the updated toggles are available
+            assertThat(provider.getOctopusContext().getContentHash()).isEqualTo(updatedHash);
+            assertThat(provider.getOctopusContext().evaluate("test-feature", true, null).getValue()).isFalse();
+
+        } finally {
+            provider.shutdown();
+        }
+    }
+
+    @Test
+    void whenInitialized_AndRefreshFails_RetainsExistingContextAndLogsError() throws InterruptedException {
+
+        byte[] contentHash = {0x01, 0x02, 0x03, 0x04};
+
+        var client = new MockOctopusFeatureClient(new FeatureToggles(
+            List.of(new FeatureToggleEvaluation("test-feature", true, "evaluation-key", Collections.emptyList(), 100)),
+            contentHash
+        ));
+
+        var logMessages = new ArrayList<String>();
+        var julLogger = Logger.getLogger(OctopusClient.class.getName());
+        var handler = new Handler() {
+            @Override public void publish(LogRecord record) { logMessages.add(record.getMessage()); }
+            @Override public void flush() {}
+            @Override public void close() {}
+        };
+        julLogger.addHandler(handler);
+
+        var provider = new OctopusContextProvider(configuration, client);
+
+        try {
+            provider.initialize();
+
+            // Simulate a failed fetch
+            client.changeToggles(null);
+
+            // Wait for the cache to expire
+            Thread.sleep(500);
+
+            // Validate that the existing context is retained and an error was logged
+            assertThat(provider.getOctopusContext().getContentHash()).isEqualTo(contentHash);
+            assertThat(provider.getOctopusContext().evaluate("test-feature", false, null).getValue()).isTrue();
+            assertThat(logMessages).anyMatch(m -> m.startsWith("Failed to retrieve updated feature manifest"));
+
+        } finally {
+            julLogger.removeHandler(handler);
+            provider.shutdown();
+        }
+    }
+}