diff --git a/demo/src/main/java/com/google/android/fhir/demo/PatientDetailsViewModel.kt b/demo/src/main/java/com/google/android/fhir/demo/PatientDetailsViewModel.kt
index 14336bba7f..014177a327 100644
--- a/demo/src/main/java/com/google/android/fhir/demo/PatientDetailsViewModel.kt
+++ b/demo/src/main/java/com/google/android/fhir/demo/PatientDetailsViewModel.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,7 +26,6 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.viewModelScope
 import com.google.android.fhir.FhirEngine
-import com.google.android.fhir.logicalId
 import com.google.android.fhir.search.revInclude
 import com.google.android.fhir.search.search
 import java.text.SimpleDateFormat
@@ -379,3 +378,12 @@ data class RiskAssessmentItem(
   var lastContacted: String,
   var patientCardColor: Int,
 )
+
+/**
+ * The logical (unqualified) part of the ID. For example, if the ID is
+ * "http://example.com/fhir/Patient/123/_history/456", then this value would be "123".
+ */
+private val Resource.logicalId: String
+  get() {
+    return this.idElement?.idPart.orEmpty()
+  }
diff --git a/engine/src/main/java/com/google/android/fhir/ContentTypes.kt b/engine/src/main/java/com/google/android/fhir/ContentTypes.kt
index eaad96cf1b..6a491d04c0 100644
--- a/engine/src/main/java/com/google/android/fhir/ContentTypes.kt
+++ b/engine/src/main/java/com/google/android/fhir/ContentTypes.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2021 Google LLC
+ * Copyright 2021-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,11 +18,11 @@ package com.google.android.fhir
 
 import okhttp3.MediaType.Companion.toMediaType
 
-object ContentTypes {
+internal object ContentTypes {
   const val APPLICATION_JSON_PATCH = "application/json-patch+json"
   const val APPLICATION_FHIR_JSON = "application/fhir+json"
 }
 
-object MediaTypes {
+internal object MediaTypes {
   val MEDIA_TYPE_FHIR_JSON = ContentTypes.APPLICATION_FHIR_JSON.toMediaType()
 }
diff --git a/engine/src/main/java/com/google/android/fhir/DateProvider.kt b/engine/src/main/java/com/google/android/fhir/DateProvider.kt
index 9d98095f95..b62ea0d7d2 100644
--- a/engine/src/main/java/com/google/android/fhir/DateProvider.kt
+++ b/engine/src/main/java/com/google/android/fhir/DateProvider.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2021-2023 Google LLC
+ * Copyright 2021-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,7 +21,7 @@ import java.time.Instant
 import java.time.ZoneId
 
 /** The DateProvider Instance [FhirEngine] uses for date/time related operations. */
-object DateProvider {
+internal object DateProvider {
   lateinit var clock: Clock
   private var fixed = false
   // TODO possibly provide more customization options
diff --git a/engine/src/main/java/com/google/android/fhir/FhirEngineProvider.kt b/engine/src/main/java/com/google/android/fhir/FhirEngineProvider.kt
index 076c0e27ed..ae3ab614fe 100644
--- a/engine/src/main/java/com/google/android/fhir/FhirEngineProvider.kt
+++ b/engine/src/main/java/com/google/android/fhir/FhirEngineProvider.kt
@@ -125,7 +125,7 @@ object FhirEngineProvider {
  * `enableEncryptionIfSupported` is true, the FHIR SDK will only enable database encryption on
  * supported devices.
  *
- * WARNING: If database encryption is enabled, devices that are on API 22 (Android 5.1) or lower
+ * **WARNING:** If database encryption is enabled, devices that are on API 22 (Android 5.1) or lower
  * will have an unencrypted database. If those devices are later updated to API 23 or newer, they
  * will encounter an `IllegalStateException`. This is because the database was created without
  * encryption on the older API level, and enabling encryption in the new release will not
@@ -143,11 +143,10 @@ object FhirEngineProvider {
  *   engine with the Search API. These are in addition to the default
  *   [search parameters](https://www.hl7.org/fhir/searchparameter-registry.html) defined in the FHIR
  *   specification. Custom search parameters must be unique and not change existing or default
- *   search parameters.
- *
- * Note: The engine does not automatically reindex resources after new custom search parameters are
- * added. You must manually reindex resources by updating them. Any new CRUD operations on a
- * resource after adding new search parameters will automatically trigger reindexing.
+ *   search parameters.<p> **Note:** The engine does not automatically reindex resources after new
+ *   custom search parameters are added. You must manually reindex resources by updating them. Any
+ *   new CRUD operations on a resource after adding new search parameters will automatically trigger
+ *   reindexing.
  */
 data class FhirEngineConfiguration(
   val enableEncryptionIfSupported: Boolean = false,
@@ -157,6 +156,7 @@ data class FhirEngineConfiguration(
   val customSearchParameters: List<SearchParameter>? = null,
 )
 
+/** How database errors should be handled. */
 enum class DatabaseErrorStrategy {
   /**
    * If unspecified, all database errors will be propagated to the call site. The caller shall
diff --git a/engine/src/main/java/com/google/android/fhir/LocalChange.kt b/engine/src/main/java/com/google/android/fhir/LocalChange.kt
index c790e95862..e1e7d7c8a0 100644
--- a/engine/src/main/java/com/google/android/fhir/LocalChange.kt
+++ b/engine/src/main/java/com/google/android/fhir/LocalChange.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022-2023 Google LLC
+ * Copyright 2022-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
diff --git a/engine/src/main/java/com/google/android/fhir/Util.kt b/engine/src/main/java/com/google/android/fhir/Util.kt
index 5c9dc0f69f..5ad65a52e9 100644
--- a/engine/src/main/java/com/google/android/fhir/Util.kt
+++ b/engine/src/main/java/com/google/android/fhir/Util.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 Google LLC
+ * Copyright 2022-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,7 +50,7 @@ internal fun isValidDateOnly(date: String) =
  * The logical (unqualified) part of the ID. For example, if the ID is
  * "http://example.com/fhir/Patient/123/_history/456", then this value would be "123".
  */
-val Resource.logicalId: String
+internal val Resource.logicalId: String
   get() {
     return this.idElement?.idPart.orEmpty()
   }
@@ -62,14 +62,14 @@ val Resource.logicalId: String
  * operation success/failure. TODO: pass along the HTTP result (or any other signal) to determine
  * the outcome of an instance level RESTful operation.
  */
-fun Resource.isUploadSuccess(): Boolean {
+internal fun Resource.isUploadSuccess(): Boolean {
   if (!this.resourceType.equals(ResourceType.OperationOutcome)) return false
   val outcome: OperationOutcome = this as OperationOutcome
   return outcome.issue.isNotEmpty() &&
     outcome.issue.all { it.severity.equals(OperationOutcome.IssueSeverity.INFORMATION) }
 }
 
-class OffsetDateTimeTypeAdapter : TypeAdapter<OffsetDateTime>() {
+internal class OffsetDateTimeTypeAdapter : TypeAdapter<OffsetDateTime>() {
   override fun write(out: JsonWriter, value: OffsetDateTime) {
     out.value(DateTimeFormatter.ISO_OFFSET_DATE_TIME.format(value))
   }
@@ -78,7 +78,7 @@ class OffsetDateTimeTypeAdapter : TypeAdapter<OffsetDateTime>() {
 }
 
 /** Url for the UCUM system of measures. */
-const val ucumUrl = "http://unitsofmeasure.org"
+internal const val ucumUrl = "http://unitsofmeasure.org"
 
 internal fun percentOf(value: Number, total: Number) =
   if (total == 0) 0.0 else value.toDouble() / total.toDouble()
diff --git a/engine/src/main/java/com/google/android/fhir/db/Database.kt b/engine/src/main/java/com/google/android/fhir/db/Database.kt
index 0107f67d2f..251bf21b6c 100644
--- a/engine/src/main/java/com/google/android/fhir/db/Database.kt
+++ b/engine/src/main/java/com/google/android/fhir/db/Database.kt
@@ -196,12 +196,12 @@ internal interface Database {
   ): List<LocalChangeResourceReference>
 }
 
-data class ResourceWithUUID<R>(
+internal data class ResourceWithUUID<R>(
   val uuid: UUID,
   val resource: R,
 )
 
-data class LocalChangeResourceReference(
+internal data class LocalChangeResourceReference(
   val localChangeId: Long,
   val resourceReferenceValue: String,
   val resourceReferencePath: String?,
diff --git a/engine/src/main/java/com/google/android/fhir/db/impl/DatabaseImpl.kt b/engine/src/main/java/com/google/android/fhir/db/impl/DatabaseImpl.kt
index b156b46728..2e14ea6b1d 100644
--- a/engine/src/main/java/com/google/android/fhir/db/impl/DatabaseImpl.kt
+++ b/engine/src/main/java/com/google/android/fhir/db/impl/DatabaseImpl.kt
@@ -444,7 +444,7 @@ internal class DatabaseImpl(
   }
 }
 
-data class DatabaseConfig(
+internal data class DatabaseConfig(
   val inMemory: Boolean,
   val enableEncryption: Boolean,
   val databaseErrorStrategy: DatabaseErrorStrategy,
diff --git a/engine/src/main/java/com/google/android/fhir/db/impl/ResourceDatabase.kt b/engine/src/main/java/com/google/android/fhir/db/impl/ResourceDatabase.kt
index 3502ab0b8e..158bb4b146 100644
--- a/engine/src/main/java/com/google/android/fhir/db/impl/ResourceDatabase.kt
+++ b/engine/src/main/java/com/google/android/fhir/db/impl/ResourceDatabase.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -64,14 +64,14 @@ internal abstract class ResourceDatabase : RoomDatabase() {
   abstract fun localChangeDao(): LocalChangeDao
 }
 
-val MIGRATION_1_2 =
+internal val MIGRATION_1_2 =
   object : Migration(1, 2) {
     override fun migrate(database: SupportSQLiteDatabase) {
       database.execSQL("DROP table if exists SyncedResourceEntity")
     }
   }
 
-val MIGRATION_2_3 =
+internal val MIGRATION_2_3 =
   object : Migration(2, 3) {
     override fun migrate(database: SupportSQLiteDatabase) {
       database.execSQL(
@@ -80,7 +80,7 @@ val MIGRATION_2_3 =
     }
   }
 
-val MIGRATION_3_4 =
+internal val MIGRATION_3_4 =
   object : Migration(3, 4) {
     override fun migrate(database: SupportSQLiteDatabase) {
       database.execSQL(
@@ -105,7 +105,7 @@ val MIGRATION_3_4 =
     }
   }
 
-val MIGRATION_4_5 =
+internal val MIGRATION_4_5 =
   object : Migration(4, 5) {
     override fun migrate(database: SupportSQLiteDatabase) {
       database.execSQL(
@@ -115,7 +115,7 @@ val MIGRATION_4_5 =
   }
 
 /** Changes column type of [LocalChangeEntity.timestamp] from [String] to [java.time.Instant]. */
-val MIGRATION_5_6 =
+internal val MIGRATION_5_6 =
   object : Migration(5, 6) {
     override fun migrate(database: SupportSQLiteDatabase) {
       database.execSQL(
@@ -133,7 +133,7 @@ val MIGRATION_5_6 =
   }
 
 /** Add column resourceUuid in [LocalChangeEntity] */
-val MIGRATION_6_7 =
+internal val MIGRATION_6_7 =
   object : Migration(6, 7) {
     override fun migrate(database: SupportSQLiteDatabase) {
       database.execSQL(
@@ -155,7 +155,7 @@ val MIGRATION_6_7 =
   }
 
 /** Create [LocalChangeResourceReferenceEntity] */
-val MIGRATION_7_8 =
+internal val MIGRATION_7_8 =
   object : Migration(7, 8) {
     override fun migrate(database: SupportSQLiteDatabase) {
       database.execSQL(
diff --git a/engine/src/main/java/com/google/android/fhir/db/impl/SQLCipherSupportHelper.kt b/engine/src/main/java/com/google/android/fhir/db/impl/SQLCipherSupportHelper.kt
index eaf8393d51..f761656e11 100644
--- a/engine/src/main/java/com/google/android/fhir/db/impl/SQLCipherSupportHelper.kt
+++ b/engine/src/main/java/com/google/android/fhir/db/impl/SQLCipherSupportHelper.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,7 +33,7 @@ import net.sqlcipher.database.SQLiteOpenHelper
 import timber.log.Timber
 
 /** A [SupportSQLiteOpenHelper] which initializes a [SQLiteDatabase] with a passphrase. */
-class SQLCipherSupportHelper(
+internal class SQLCipherSupportHelper(
   private val configuration: SupportSQLiteOpenHelper.Configuration,
   hook: SQLiteDatabaseHook? = null,
   private val databaseErrorStrategy: DatabaseErrorStrategy,
diff --git a/engine/src/main/java/com/google/android/fhir/index/DualHapiWorkerContext.kt b/engine/src/main/java/com/google/android/fhir/index/DualHapiWorkerContext.kt
index bfd12c5422..02306848ce 100644
--- a/engine/src/main/java/com/google/android/fhir/index/DualHapiWorkerContext.kt
+++ b/engine/src/main/java/com/google/android/fhir/index/DualHapiWorkerContext.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,7 +27,7 @@ import org.hl7.fhir.r4.model.Resource
  *
  * TODO: Ideally we update the upstream's HapiWorkerContext to support ucumServices.
  */
-class DualHapiWorkerContext : SimpleWorkerContext() {
+internal class DualHapiWorkerContext : SimpleWorkerContext() {
   val hapi =
     HapiWorkerContext(
       FhirContext.forR4Cached(),
diff --git a/engine/src/main/java/com/google/android/fhir/index/ResourceIndexer.kt b/engine/src/main/java/com/google/android/fhir/index/ResourceIndexer.kt
index b1c3f81468..8e07a8b5ae 100644
--- a/engine/src/main/java/com/google/android/fhir/index/ResourceIndexer.kt
+++ b/engine/src/main/java/com/google/android/fhir/index/ResourceIndexer.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -389,4 +389,8 @@ internal class ResourceIndexer(
   }
 }
 
-data class SearchParamDefinition(val name: String, val type: SearchParamType, val path: String)
+internal data class SearchParamDefinition(
+  val name: String,
+  val type: SearchParamType,
+  val path: String,
+)
diff --git a/engine/src/main/java/com/google/android/fhir/index/entities/PositionIndex.kt b/engine/src/main/java/com/google/android/fhir/index/entities/PositionIndex.kt
index d052326ef5..f6bcfcc161 100644
--- a/engine/src/main/java/com/google/android/fhir/index/entities/PositionIndex.kt
+++ b/engine/src/main/java/com/google/android/fhir/index/entities/PositionIndex.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2021 Google LLC
+ * Copyright 2021-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,4 +21,4 @@ package com.google.android.fhir.index.entities
  *
  * See https://www.hl7.org/fhir/search.html#special.
  */
-data class PositionIndex(val latitude: Double, val longitude: Double)
+internal data class PositionIndex(val latitude: Double, val longitude: Double)
diff --git a/engine/src/main/java/com/google/android/fhir/search/query/XFhirQueryTranslator.kt b/engine/src/main/java/com/google/android/fhir/search/query/XFhirQueryTranslator.kt
index ce158d32d9..9681728c0a 100644
--- a/engine/src/main/java/com/google/android/fhir/search/query/XFhirQueryTranslator.kt
+++ b/engine/src/main/java/com/google/android/fhir/search/query/XFhirQueryTranslator.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022-2023 Google LLC
+ * Copyright 2022-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -44,7 +44,7 @@ import org.hl7.fhir.r4.model.ResourceType
  * http://build.fhir.org/ig/HL7/sdc/expressions.html#x-fhir-query-enhancements and
  * http://hl7.org/fhir/R4/search.html
  */
-object XFhirQueryTranslator {
+internal object XFhirQueryTranslator {
   private const val XFHIR_QUERY_SORT_PARAM = "_sort"
   private const val XFHIR_QUERY_COUNT_PARAM = "_count"
 
diff --git a/engine/src/main/java/com/google/android/fhir/sync/remote/FhirConverterFactory.kt b/engine/src/main/java/com/google/android/fhir/sync/remote/FhirConverterFactory.kt
index fc2fab0c70..bd8fbe63f3 100644
--- a/engine/src/main/java/com/google/android/fhir/sync/remote/FhirConverterFactory.kt
+++ b/engine/src/main/java/com/google/android/fhir/sync/remote/FhirConverterFactory.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
diff --git a/engine/src/main/java/com/google/android/fhir/sync/upload/patch/Patch.kt b/engine/src/main/java/com/google/android/fhir/sync/upload/patch/Patch.kt
index bf3b6fac68..103aaac1bf 100644
--- a/engine/src/main/java/com/google/android/fhir/sync/upload/patch/Patch.kt
+++ b/engine/src/main/java/com/google/android/fhir/sync/upload/patch/Patch.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,7 +21,7 @@ import java.time.Instant
 import org.hl7.fhir.r4.model.Resource
 
 /** Data class for squashed local changes for resource */
-data class Patch(
+internal data class Patch(
   /** The [ResourceType] */
   val resourceType: String,
   /** The resource id [Resource.id] */
diff --git a/engine/src/main/java/com/google/android/fhir/sync/upload/request/BundleEntryComponentGenerator.kt b/engine/src/main/java/com/google/android/fhir/sync/upload/request/BundleEntryComponentGenerator.kt
index 372ed59c93..329a2965a9 100644
--- a/engine/src/main/java/com/google/android/fhir/sync/upload/request/BundleEntryComponentGenerator.kt
+++ b/engine/src/main/java/com/google/android/fhir/sync/upload/request/BundleEntryComponentGenerator.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,7 +30,7 @@ import org.hl7.fhir.r4.model.UriType
  * [LocalChangeEntity]. See [https://www.hl7.org/fhir/http.html#transaction] for more info regarding
  * the supported [Bundle.HTTPVerb].
  */
-abstract class BundleEntryComponentGenerator(
+internal abstract class BundleEntryComponentGenerator(
   private val httpVerb: Bundle.HTTPVerb,
   private val useETagForUpload: Boolean,
 ) {
diff --git a/engine/src/main/java/com/google/android/fhir/testing/Utilities.kt b/engine/src/main/java/com/google/android/fhir/testing/Utilities.kt
index e6c0441158..c99e17be73 100644
--- a/engine/src/main/java/com/google/android/fhir/testing/Utilities.kt
+++ b/engine/src/main/java/com/google/android/fhir/testing/Utilities.kt
@@ -55,21 +55,21 @@ import org.hl7.fhir.r4.model.ResourceType
 import org.json.JSONArray
 import org.json.JSONObject
 
-val jsonParser: IParser = FhirContext.forCached(FhirVersionEnum.R4).newJsonParser()
+internal val jsonParser: IParser = FhirContext.forCached(FhirVersionEnum.R4).newJsonParser()
 
 /** Asserts that the `expected` and the `actual` FHIR resources are equal. */
-fun assertResourceEquals(expected: Resource?, actual: Resource?) {
+internal fun assertResourceEquals(expected: Resource?, actual: Resource?) {
   assertThat(jsonParser.encodeResourceToString(actual))
     .isEqualTo(jsonParser.encodeResourceToString(expected))
 }
 
 /** Asserts that the `expected` and the `actual` FHIR resources are not equal. */
-fun assertResourceNotEquals(expected: Resource?, actual: Resource?) {
+internal fun assertResourceNotEquals(expected: Resource?, actual: Resource?) {
   assertThat(jsonParser.encodeResourceToString(actual))
     .isNotEqualTo(jsonParser.encodeResourceToString(expected))
 }
 
-fun assertJsonArrayEqualsIgnoringOrder(actual: JSONArray, expected: JSONArray) {
+internal fun assertJsonArrayEqualsIgnoringOrder(actual: JSONArray, expected: JSONArray) {
   assertThat(actual.length()).isEqualTo(expected.length())
   val actuals = mutableListOf<String>()
   val expecteds = mutableListOf<String>()
@@ -83,7 +83,7 @@ fun assertJsonArrayEqualsIgnoringOrder(actual: JSONArray, expected: JSONArray) {
 }
 
 /** Reads a [Resource] from given file in the `sampledata` dir */
-fun <R : Resource> readFromFile(clazz: Class<R>, filename: String): R {
+internal fun <R : Resource> readFromFile(clazz: Class<R>, filename: String): R {
   val resourceJson = readJsonFromFile(filename)
   return jsonParser.parseResource(clazz, resourceJson.toString()) as R
 }
@@ -96,13 +96,13 @@ private fun readJsonFromFile(filename: String): JSONObject {
 }
 
 /** Reads a [JSONArray] from given file in the `sampledata` dir */
-fun readJsonArrayFromFile(filename: String): JSONArray {
+internal fun readJsonArrayFromFile(filename: String): JSONArray {
   val inputStream = {}.javaClass.getResourceAsStream(filename)
   val content = inputStream!!.bufferedReader(Charsets.UTF_8).readText()
   return JSONArray(content)
 }
 
-object TestDataSourceImpl : DataSource {
+internal object TestDataSourceImpl : DataSource {
 
   override suspend fun download(downloadRequest: DownloadRequest) =
     when (downloadRequest) {
@@ -120,7 +120,7 @@ object TestDataSourceImpl : DataSource {
   }
 }
 
-open class TestDownloadManagerImpl(
+internal open class TestDownloadManagerImpl(
   private val queries: List<String> = listOf("Patient?address-city=NAIROBI"),
 ) : DownloadWorkManager {
   private val urls = LinkedList(queries)
@@ -141,7 +141,7 @@ open class TestDownloadManagerImpl(
   }
 }
 
-object TestFhirEngineImpl : FhirEngine {
+internal object TestFhirEngineImpl : FhirEngine {
   override suspend fun create(vararg resource: Resource) = emptyList<String>()
 
   override suspend fun update(vararg resource: Resource) {}
@@ -204,7 +204,7 @@ object TestFhirEngineImpl : FhirEngine {
   override suspend fun purge(type: ResourceType, ids: Set<String>, forcePurge: Boolean) {}
 }
 
-object TestFailingDatasource : DataSource {
+internal object TestFailingDatasource : DataSource {
 
   override suspend fun download(downloadRequest: DownloadRequest) =
     when (downloadRequest) {
@@ -223,7 +223,8 @@ object TestFailingDatasource : DataSource {
   }
 }
 
-class BundleDataSource(val onPostBundle: suspend (BundleUploadRequest) -> Resource) : DataSource {
+internal class BundleDataSource(val onPostBundle: suspend (BundleUploadRequest) -> Resource) :
+  DataSource {
 
   override suspend fun download(downloadRequest: DownloadRequest): Resource {
     TODO("Not yet implemented")
@@ -233,7 +234,7 @@ class BundleDataSource(val onPostBundle: suspend (BundleUploadRequest) -> Resour
     onPostBundle((request as BundleUploadRequest))
 }
 
-class UrlRequestDataSource(val onUrlRequestSend: suspend (UrlUploadRequest) -> Resource) :
+internal class UrlRequestDataSource(val onUrlRequestSend: suspend (UrlUploadRequest) -> Resource) :
   DataSource {
 
   override suspend fun download(downloadRequest: DownloadRequest): Resource {
diff --git a/engine/src/test/java/com/google/android/fhir/sync/FhirSyncWorkerTest.kt b/engine/src/test/java/com/google/android/fhir/sync/FhirSyncWorkerTest.kt
index 8932338bb1..ba51d5d5e6 100644
--- a/engine/src/test/java/com/google/android/fhir/sync/FhirSyncWorkerTest.kt
+++ b/engine/src/test/java/com/google/android/fhir/sync/FhirSyncWorkerTest.kt
@@ -42,7 +42,7 @@ import org.robolectric.annotation.Config
 
 @RunWith(RobolectricTestRunner::class)
 @Config(manifest = Config.NONE)
-class FhirSyncWorkerTest {
+internal class FhirSyncWorkerTest {
   private lateinit var context: Context
 
   class PassingPeriodicSyncWorker(appContext: Context, workerParams: WorkerParameters) :
diff --git a/engine/src/test/java/com/google/android/fhir/sync/upload/request/RequestGeneratorTestUtils.kt b/engine/src/test/java/com/google/android/fhir/sync/upload/request/RequestGeneratorTestUtils.kt
index 6f8bc949dd..b9ea837690 100644
--- a/engine/src/test/java/com/google/android/fhir/sync/upload/request/RequestGeneratorTestUtils.kt
+++ b/engine/src/test/java/com/google/android/fhir/sync/upload/request/RequestGeneratorTestUtils.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 Google LLC
+ * Copyright 2023-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,7 +26,7 @@ import org.hl7.fhir.r4.model.HumanName
 import org.hl7.fhir.r4.model.Patient
 import org.hl7.fhir.r4.model.ResourceType
 
-object RequestGeneratorTestUtils {
+internal object RequestGeneratorTestUtils {
 
   fun LocalChange.toPatch() =
     Patch(