diff --git a/core/definitions.mk b/core/definitions.mk
index 462c968..62d482b 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -3203,8 +3203,9 @@
 define copy-vintf-manifest-checked
 $(2): $(1) $(HOST_OUT_EXECUTABLES)/assemble_vintf
 	@echo "Copy xml: $$@"
-	$(hide) $(HOST_OUT_EXECUTABLES)/assemble_vintf -i $$< >/dev/null  # Don't print the xml file to stdout.
-	$$(copy-file-to-target)
+	$(hide) mkdir -p "$$(dir $$@)"
+	$(hide) VINTF_IGNORE_TARGET_FCM_VERSION=true\
+		$(HOST_OUT_EXECUTABLES)/assemble_vintf -i $$< -o $$@
 endef
 
 # Copies many vintf manifest files checked.
diff --git a/tools/aconfig/Android.bp b/tools/aconfig/Android.bp
index a4ea7f4..93fd6f7 100644
--- a/tools/aconfig/Android.bp
+++ b/tools/aconfig/Android.bp
@@ -101,7 +101,7 @@
 android_test {
     name: "aconfig.test.java",
     srcs: [
-        "tests/**/*.java",
+        "tests/AconfigTest.java",
     ],
     manifest: "tests/AndroidManifest.xml",
     certificate: "platform",
@@ -113,6 +113,25 @@
     test_suites: ["device-tests"],
 }
 
+java_aconfig_library {
+    name: "aconfig_host_test_java_library",
+    aconfig_declarations: "aconfig.test.flags",
+    host_supported: true,
+    test: true,
+}
+
+java_test_host {
+    name: "AconfigJavaHostTest",
+    srcs: [
+        "tests/AconfigHostTest.java",
+    ],
+    static_libs: [
+        "aconfig_host_test_java_library",
+        "junit",
+    ],
+    test_suites: ["general-tests"],
+}
+
 // integration tests: C++
 
 cc_aconfig_library {
diff --git a/tools/aconfig/src/codegen_java.rs b/tools/aconfig/src/codegen_java.rs
index 8ab6ffa..2c9dcf5 100644
--- a/tools/aconfig/src/codegen_java.rs
+++ b/tools/aconfig/src/codegen_java.rs
@@ -47,9 +47,13 @@
         "FeatureFlags.java",
         include_str!("../templates/FeatureFlags.java.template"),
     )?;
+    template.add_template(
+        "FakeFeatureFlagsImpl.java",
+        include_str!("../templates/FakeFeatureFlagsImpl.java.template"),
+    )?;
 
     let path: PathBuf = package.split('.').collect();
-    ["Flags.java", "FeatureFlagsImpl.java", "FeatureFlags.java"]
+    ["Flags.java", "FeatureFlags.java", "FeatureFlagsImpl.java", "FakeFeatureFlagsImpl.java"]
         .iter()
         .map(|file| {
             Ok(OutputFile {
@@ -112,14 +116,14 @@
     use super::*;
     use std::collections::HashMap;
 
-    const EXPECTED_FEATUREFLAGS_CONTENT: &str = r#"
+    const EXPECTED_FEATUREFLAGS_COMMON_CONTENT: &str = r#"
     package com.android.aconfig.test;
     public interface FeatureFlags {
         boolean disabledRo();
         boolean disabledRw();
         boolean enabledRo();
         boolean enabledRw();
-    }"#;
+    "#;
 
     const EXPECTED_FLAG_COMMON_CONTENT: &str = r#"
     package com.android.aconfig.test;
@@ -143,6 +147,29 @@
         }
     "#;
 
+    const EXPECTED_METHOD_NOT_IMPL_COMMON_CONTENT: &str = r#"
+        @Override
+        public boolean disabledRo() {
+            throw new UnsupportedOperationException(
+                "Method is not implemented.");
+        }
+        @Override
+        public boolean disabledRw() {
+            throw new UnsupportedOperationException(
+                "Method is not implemented.");
+        }
+        @Override
+        public boolean enabledRo() {
+            throw new UnsupportedOperationException(
+                "Method is not implemented.");
+        }
+        @Override
+        public boolean enabledRw() {
+            throw new UnsupportedOperationException(
+                "Method is not implemented.");
+        }
+    "#;
+
     #[test]
     fn test_generate_java_code_production() {
         let parsed_flags = crate::test::parse_test_flags();
@@ -152,11 +179,22 @@
             CodegenMode::Production,
         )
         .unwrap();
+        let expect_featureflags_content = EXPECTED_FEATUREFLAGS_COMMON_CONTENT.to_string()
+            + r#"
+        }"#;
         let expect_flags_content = EXPECTED_FLAG_COMMON_CONTENT.to_string()
             + r#"
             private static FeatureFlags FEATURE_FLAGS = new FeatureFlagsImpl();
         }"#;
-        let expected_featureflagsimpl_content = r#"
+        let expect_fakefeatureflagsimpl_content = r#"
+        package com.android.aconfig.test;
+        public class FakeFeatureFlagsImpl implements FeatureFlags {"#
+            .to_owned()
+            + EXPECTED_METHOD_NOT_IMPL_COMMON_CONTENT
+            + r#"
+        }
+        "#;
+        let expect_featureflagsimpl_content = r#"
         package com.android.aconfig.test;
         import android.provider.DeviceConfig;
         public final class FeatureFlagsImpl implements FeatureFlags {
@@ -188,8 +226,12 @@
         "#;
         let mut file_set = HashMap::from([
             ("com/android/aconfig/test/Flags.java", expect_flags_content.as_str()),
-            ("com/android/aconfig/test/FeatureFlagsImpl.java", expected_featureflagsimpl_content),
-            ("com/android/aconfig/test/FeatureFlags.java", EXPECTED_FEATUREFLAGS_CONTENT),
+            ("com/android/aconfig/test/FeatureFlagsImpl.java", expect_featureflagsimpl_content),
+            ("com/android/aconfig/test/FeatureFlags.java", expect_featureflags_content.as_str()),
+            (
+                "com/android/aconfig/test/FakeFeatureFlagsImpl.java",
+                expect_fakefeatureflagsimpl_content.as_str(),
+            ),
         ]);
 
         for file in generated_files {
@@ -219,24 +261,47 @@
             CodegenMode::Test,
         )
         .unwrap();
+        let expect_featureflags_content = EXPECTED_FEATUREFLAGS_COMMON_CONTENT.to_string()
+            + r#"
+            public void setFlag(String flagName, boolean value);
+            public void resetAll();
+        }"#;
         let expect_flags_content = EXPECTED_FLAG_COMMON_CONTENT.to_string()
             + r#"
-            public static void setFeatureFlagsImpl(FeatureFlags featureFlags) {
+            public static void setFeatureFlags(FeatureFlags featureFlags) {
                 Flags.FEATURE_FLAGS = featureFlags;
             }
-            public static void unsetFeatureFlagsImpl() {
+            public static void unsetFeatureFlags() {
                 Flags.FEATURE_FLAGS = null;
             }
             private static FeatureFlags FEATURE_FLAGS;
         }
         "#;
-        let expected_featureflagsimpl_content = r#"
+        let expect_featureflagsimpl_content = r#"
+        package com.android.aconfig.test;
+        public final class FeatureFlagsImpl implements FeatureFlags {"#
+            .to_owned()
+            + EXPECTED_METHOD_NOT_IMPL_COMMON_CONTENT
+            + r#"
+            @Override
+            public void setFlag(String flagName, boolean value) {
+                throw new UnsupportedOperationException(
+                    "Method is not implemented.");
+            }
+            @Override
+            public void resetAll() {
+                throw new UnsupportedOperationException(
+                    "Method is not implemented.");
+            }
+        }
+        "#;
+        let expect_fakefeatureflagsimpl_content = r#"
         package com.android.aconfig.test;
         import static java.util.stream.Collectors.toMap;
         import java.util.HashMap;
         import java.util.Map;
         import java.util.stream.Stream;
-        public final class FeatureFlagsImpl implements FeatureFlags {
+        public class FakeFeatureFlagsImpl implements FeatureFlags {
             @Override
             public boolean disabledRo() {
                 return getFlag(Flags.FLAG_DISABLED_RO);
@@ -253,12 +318,14 @@
             public boolean enabledRw() {
                 return getFlag(Flags.FLAG_ENABLED_RW);
             }
+            @Override
             public void setFlag(String flagName, boolean value) {
                 if (!this.mFlagMap.containsKey(flagName)) {
                     throw new IllegalArgumentException("no such flag" + flagName);
                 }
                 this.mFlagMap.put(flagName, value);
             }
+            @Override
             public void resetAll() {
                 for (Map.Entry entry : mFlagMap.entrySet()) {
                     entry.setValue(null);
@@ -284,10 +351,18 @@
                 );
         }
         "#;
+
         let mut file_set = HashMap::from([
             ("com/android/aconfig/test/Flags.java", expect_flags_content.as_str()),
-            ("com/android/aconfig/test/FeatureFlagsImpl.java", expected_featureflagsimpl_content),
-            ("com/android/aconfig/test/FeatureFlags.java", EXPECTED_FEATUREFLAGS_CONTENT),
+            ("com/android/aconfig/test/FeatureFlags.java", expect_featureflags_content.as_str()),
+            (
+                "com/android/aconfig/test/FeatureFlagsImpl.java",
+                expect_featureflagsimpl_content.as_str(),
+            ),
+            (
+                "com/android/aconfig/test/FakeFeatureFlagsImpl.java",
+                expect_fakefeatureflagsimpl_content,
+            ),
         ]);
 
         for file in generated_files {
diff --git a/tools/aconfig/templates/FakeFeatureFlagsImpl.java.template b/tools/aconfig/templates/FakeFeatureFlagsImpl.java.template
new file mode 100644
index 0000000..dba82ef
--- /dev/null
+++ b/tools/aconfig/templates/FakeFeatureFlagsImpl.java.template
@@ -0,0 +1,61 @@
+package {package_name};
+{{ if is_test_mode }}
+import static java.util.stream.Collectors.toMap;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Stream;
+
+public class FakeFeatureFlagsImpl implements FeatureFlags \{
+{{ for item in class_elements}}
+    @Override
+    public boolean {item.method_name}() \{
+        return getFlag(Flags.FLAG_{item.flag_name_constant_suffix});
+    }
+{{ endfor}}
+    @Override
+    public void setFlag(String flagName, boolean value) \{
+        if (!this.mFlagMap.containsKey(flagName)) \{
+            throw new IllegalArgumentException("no such flag" + flagName);
+        }
+        this.mFlagMap.put(flagName, value);
+    }
+
+    @Override
+    public void resetAll() \{
+        for (Map.Entry entry : mFlagMap.entrySet()) \{
+            entry.setValue(null);
+        }
+    }
+
+    private boolean getFlag(String flagName) \{
+        Boolean value = this.mFlagMap.get(flagName);
+        if (value == null) \{
+            throw new IllegalArgumentException(flagName + " is not set");
+        }
+        return value;
+    }
+
+    private HashMap<String, Boolean> mFlagMap = Stream.of(
+            {{-for item in class_elements}}
+            Flags.FLAG_{item.flag_name_constant_suffix}{{ if not @last }},{{ endif }}
+            {{ -endfor }}
+        )
+        .collect(
+            HashMap::new,
+            (map, elem) -> map.put(elem, null),
+            HashMap::putAll
+        );
+}
+{{ else }}
+{#- Generate only stub if in prod mode #}
+public class FakeFeatureFlagsImpl implements FeatureFlags \{
+{{ for item in class_elements}}
+    @Override
+    public boolean {item.method_name}() \{
+        throw new UnsupportedOperationException(
+            "Method is not implemented.");
+    }
+{{ endfor}}
+}
+{{ endif }}
diff --git a/tools/aconfig/templates/FeatureFlags.java.template b/tools/aconfig/templates/FeatureFlags.java.template
index e0f201f..c99ccbb 100644
--- a/tools/aconfig/templates/FeatureFlags.java.template
+++ b/tools/aconfig/templates/FeatureFlags.java.template
@@ -4,4 +4,10 @@
 {{ for item in class_elements}}
     boolean {item.method_name}();
 {{ endfor }}
+
+{{ -if is_test_mode }}
+    public void setFlag(String flagName, boolean value);
+
+    public void resetAll();
+{{ -endif }}
 }
diff --git a/tools/aconfig/templates/FeatureFlagsImpl.java.template b/tools/aconfig/templates/FeatureFlagsImpl.java.template
index 082d476..7e1eb15 100644
--- a/tools/aconfig/templates/FeatureFlagsImpl.java.template
+++ b/tools/aconfig/templates/FeatureFlagsImpl.java.template
@@ -1,65 +1,44 @@
 package {package_name};
-{{ -if is_test_mode }}
-import static java.util.stream.Collectors.toMap;
-
-import java.util.HashMap;
-import java.util.Map;
-import java.util.stream.Stream;
-{{ else}}
+{{ if not is_test_mode }}
 {{ if is_read_write- }}
 import android.provider.DeviceConfig;
-{{ -endif- }}
 {{ endif }}
 public final class FeatureFlagsImpl implements FeatureFlags \{
 {{ for item in class_elements}}
     @Override
     public boolean {item.method_name}() \{
-        {{ -if not is_test_mode- }}
-        {{ if item.is_read_write }}
+    {{ -if item.is_read_write }}
         return DeviceConfig.getBoolean(
             "{item.device_config_namespace}",
             "{item.device_config_flag}",
             {item.default_value}
         );
-        {{ -else }}
+    {{ else }}
         return {item.default_value};
-        {{ -endif- }}
-        {{ else }}
-        return getFlag(Flags.FLAG_{item.flag_name_constant_suffix});
-        {{ -endif }}
+    {{ endif- }}
     }
 {{ endfor- }}
-{{ if is_test_mode }}
-    public void setFlag(String flagName, boolean value) \{
-        if (!this.mFlagMap.containsKey(flagName)) \{
-            throw new IllegalArgumentException("no such flag" + flagName);
-        }
-        this.mFlagMap.put(flagName, value);
-    }
-
-    public void resetAll() \{
-        for (Map.Entry entry : mFlagMap.entrySet()) \{
-            entry.setValue(null);
-        }
-    }
-
-    private boolean getFlag(String flagName) \{
-        Boolean value = this.mFlagMap.get(flagName);
-        if (value == null) \{
-            throw new IllegalArgumentException(flagName + " is not set");
-        }
-        return value;
-    }
-
-    private HashMap<String, Boolean> mFlagMap = Stream.of(
-            {{-for item in class_elements}}
-            Flags.FLAG_{item.flag_name_constant_suffix}{{ if not @last }},{{ endif }}
-            {{ -endfor }}
-        )
-        .collect(
-            HashMap::new,
-            (map, elem) -> map.put(elem, null),
-            HashMap::putAll
-        );
-{{ -endif }}
 }
+{{ else }}
+{#- Generate only stub if in test mode #}
+public final class FeatureFlagsImpl implements FeatureFlags \{
+{{ for item in class_elements}}
+    @Override
+    public boolean {item.method_name}() \{
+        throw new UnsupportedOperationException(
+            "Method is not implemented.");
+    }
+{{ endfor- }}
+    @Override
+    public void setFlag(String flagName, boolean value) \{
+        throw new UnsupportedOperationException(
+            "Method is not implemented.");
+    }
+
+    @Override
+    public void resetAll() \{
+        throw new UnsupportedOperationException(
+            "Method is not implemented.");
+    }
+}
+{{ endif }}
diff --git a/tools/aconfig/templates/Flags.java.template b/tools/aconfig/templates/Flags.java.template
index c244b15..012eba6 100644
--- a/tools/aconfig/templates/Flags.java.template
+++ b/tools/aconfig/templates/Flags.java.template
@@ -10,11 +10,11 @@
     }
 {{ endfor }}
 {{ -if is_test_mode }}
-    public static void setFeatureFlagsImpl(FeatureFlags featureFlags) \{
+    public static void setFeatureFlags(FeatureFlags featureFlags) \{
         Flags.FEATURE_FLAGS = featureFlags;
     }
 
-    public static void unsetFeatureFlagsImpl() \{
+    public static void unsetFeatureFlags() \{
         Flags.FEATURE_FLAGS = null;
     }
 {{ endif}}
diff --git a/tools/aconfig/tests/AconfigHostTest.java b/tools/aconfig/tests/AconfigHostTest.java
new file mode 100644
index 0000000..29a01e3
--- /dev/null
+++ b/tools/aconfig/tests/AconfigHostTest.java
@@ -0,0 +1,88 @@
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+
+import com.android.aconfig.test.FakeFeatureFlagsImpl;
+import com.android.aconfig.test.FeatureFlags;
+import com.android.aconfig.test.FeatureFlagsImpl;
+import com.android.aconfig.test.Flags;
+
+@RunWith(JUnit4.class)
+public final class AconfigHostTest {
+    @Test
+    public void testThrowsExceptionIfFlagNotSet() {
+        assertThrows(NullPointerException.class, () -> Flags.disabledRo());
+        FeatureFlags featureFlags = new FakeFeatureFlagsImpl();
+        assertThrows(IllegalArgumentException.class, () -> featureFlags.disabledRo());
+    }
+
+    @Test
+    public void testSetFlagInFakeFeatureFlagsImpl() {
+        FeatureFlags featureFlags = new FakeFeatureFlagsImpl();
+        featureFlags.setFlag(Flags.FLAG_ENABLED_RW, true);
+        assertTrue(featureFlags.enabledRw());
+        featureFlags.setFlag(Flags.FLAG_ENABLED_RW, false);
+        assertFalse(featureFlags.enabledRw());
+
+        //Set Flags
+        assertThrows(NullPointerException.class, () -> Flags.enabledRw());
+        Flags.setFeatureFlags(featureFlags);
+        featureFlags.setFlag(Flags.FLAG_ENABLED_RW, true);
+        assertTrue(Flags.enabledRw());
+        Flags.unsetFeatureFlags();
+    }
+
+    @Test
+    public void testSetFlagWithRandomName() {
+        FeatureFlags featureFlags = new FakeFeatureFlagsImpl();
+        assertThrows(IllegalArgumentException.class,
+            () -> featureFlags.setFlag("Randome_name", true));
+    }
+
+    @Test
+    public void testResetFlagsInFakeFeatureFlagsImpl() {
+        FeatureFlags featureFlags = new FakeFeatureFlagsImpl();
+        featureFlags.setFlag(Flags.FLAG_ENABLED_RO, true);
+        assertTrue(featureFlags.enabledRo());
+        featureFlags.resetAll();
+        assertThrows(IllegalArgumentException.class, () -> featureFlags.enabledRo());
+
+        // Set value after reset
+        featureFlags.setFlag(Flags.FLAG_ENABLED_RO, false);
+        assertFalse(featureFlags.enabledRo());
+    }
+
+    @Test
+    public void testFlagsSetFeatureFlags() {
+        FeatureFlags featureFlags = new FakeFeatureFlagsImpl();
+        featureFlags.setFlag(Flags.FLAG_ENABLED_RW, true);
+        assertThrows(NullPointerException.class, () -> Flags.enabledRw());
+        Flags.setFeatureFlags(featureFlags);
+        assertTrue(Flags.enabledRw());
+        Flags.unsetFeatureFlags();
+    }
+
+    @Test
+    public void testFlagsUnsetFeatureFlags() {
+        FeatureFlags featureFlags = new FakeFeatureFlagsImpl();
+        featureFlags.setFlag(Flags.FLAG_ENABLED_RW, true);
+        assertThrows(NullPointerException.class, () -> Flags.enabledRw());
+        Flags.setFeatureFlags(featureFlags);
+        assertTrue(Flags.enabledRw());
+
+        Flags.unsetFeatureFlags();
+        assertThrows(NullPointerException.class, () -> Flags.enabledRw());
+    }
+
+    @Test
+    public void testFeatureFlagsImplNotImpl() {
+        FeatureFlags featureFlags = new FeatureFlagsImpl();
+        assertThrows(UnsupportedOperationException.class,
+            () -> featureFlags.enabledRw());
+    }
+}
diff --git a/tools/aconfig/tests/AconfigTest.java b/tools/aconfig/tests/AconfigTest.java
index 6681f32..317289d 100644
--- a/tools/aconfig/tests/AconfigTest.java
+++ b/tools/aconfig/tests/AconfigTest.java
@@ -8,12 +8,16 @@
 import static com.android.aconfig.test.Flags.enabledRw;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
+import com.android.aconfig.test.FakeFeatureFlagsImpl;
+import com.android.aconfig.test.FeatureFlags;
+
 @RunWith(JUnit4.class)
 public final class AconfigTest {
     @Test
@@ -43,4 +47,10 @@
         // (currently all flags are assigned the default READ_ONLY + DISABLED)
         assertFalse(enabledRw());
     }
+
+    @Test
+    public void testFakeFeatureFlagsImplNotImpl() {
+        FeatureFlags featureFlags = new FakeFeatureFlagsImpl();
+        assertThrows(UnsupportedOperationException.class, () -> featureFlags.enabledRw());
+    }
 }
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 28943fc..71dbde6 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -247,7 +247,9 @@
       older SPL.
 
   --vabc_compression_param
-      Compression algorithm to be used for VABC. Available options: gz, lz4, zstd, brotli, none
+      Compression algorithm to be used for VABC. Available options: gz, lz4, zstd, brotli, none. 
+      Compression level can be specified by appending ",$LEVEL" to option. 
+      e.g. --vabc_compression_param=gz,9 specifies level 9 compression with gz algorithm
 
   --security_patch_level
       Override the security patch level in target files
@@ -1210,7 +1212,13 @@
       assert a.lower() in ["true", "false"]
       OPTIONS.enable_lz4diff = a.lower() != "false"
     elif o == "--vabc_compression_param":
+      words = a.split(",")
+      assert len(words) >= 1 and len(words) <= 2
       OPTIONS.vabc_compression_param = a.lower()
+      if len(words) == 2:
+        if not words[1].isdigit():
+          raise ValueError("Cannot parse value %r for option $COMPRESSION_LEVEL - only "
+                         "integers are allowed." % words[1])
     elif o == "--security_patch_level":
       OPTIONS.security_patch_level = a
     elif o in ("--max_threads"):