test: Implement logic to clear LocalGcs after each test (#1661)

Fixes #1578 

Change description:
* there are only 2 tests that require pre-uploaded files -- now they upload filed on their own (`ArgsHelperTest#assertGcsFileExists succeeds` & `TestRunnerTest#mockedAndroidTestRun gcsAndHistoryName`)
* Google API provides `FakeStorageRpc` which is created with `LocalStorageHelper.getOptions()`
* `FakeStorageRpc` can be cleaned/reseted only by calling `LocalStorageHelper.getOptions()` (both its hashmaps are cleared)
* Above is, unfortunately, the only way to clear `FakeStorageRpc` -- storage has `reset` method but it's not exposed
* The `TestStorageProvider` is introduced to wrap additional test logic
* Intention behind `TestStorageProvider` is `GcStorage` should not be aware of how it is used (tests or production )
* The `TestStorageProvider` has nullable `Storage` filed. It can be cleared (set null) with `#clearStorage`
* If storage is null `TestStorageProvider` will invoke `LocalStorageHelper.getOptions()` and assign reference to storage field.
* `FlankTestRunner` has a custom listener that will invoke `LocalGcs#clear()` after each test run

## Test Plan
> How do we know the code works?

Unfortunately, there is no straightforward way to verify it since OOM error occurred only on GH Actions machines, randomly.

test_runner/src/main/kotlin/ftl/gc/GcStorage.kt

@@ -51,7 +51,7 @@ object GcStorage {
     val storage: Storage by lazy {
         GoogleApiLogger.silenceComputeEngine()
         if (FtlConstants.useMock) {
-            LocalStorageHelper.getOptions().service
+            TestStorageProvider.storage
         } else {
             storageOptions.service
         }
@@ -210,3 +210,20 @@ object GcStorage {
 
     private fun String.dropLeadingSlash() = drop(1)
 }
+
+object TestStorageProvider {
+    init {
+        require(FtlConstants.useMock) { "Storage provider can be used only during tests" }
+    }
+
+    private var backingStorage: Storage? = null
+
+    val storage: Storage
+        get() = backingStorage ?: LocalStorageHelper.getOptions().service.apply {
+            backingStorage = this
+        }
+
+    fun clearStorage() {
+        backingStorage = null
+    }
+}

test_runner/src/test/kotlin/ftl/args/ArgsHelperTest.kt

@@ -16,6 +16,7 @@ import ftl.shard.TestMethod
 import ftl.shard.TestShard
 import ftl.shard.stringShards
 import ftl.test.util.FlankTestRunner
+import ftl.test.util.LocalGcs
 import ftl.test.util.TestHelper.absolutePath
 import ftl.test.util.assertThrowsWithMessage
 import io.mockk.every
@@ -76,6 +77,10 @@ class ArgsHelperTest {
 
     @Test
     fun `assertGcsFileExists succeeds`() {
+        // given
+        LocalGcs.uploadFileForTest("../test_projects/android/apks/app-debug.apk")
+
+        // then
         assertGcsFileExists("gs://tmp_bucket_2/app-debug.apk")
     }
 

test_runner/src/test/kotlin/ftl/run/TestRunnerTest.kt

@@ -12,6 +12,7 @@ import ftl.args.IosArgs
 import ftl.http.executeWithRetry
 import ftl.run.common.getDownloadPath
 import ftl.test.util.FlankTestRunner
+import ftl.test.util.LocalGcs
 import io.mockk.every
 import io.mockk.mockk
 import io.mockk.mockkStatic
@@ -120,6 +121,11 @@ class TestRunnerTest {
 
     @Test
     fun `mockedAndroidTestRun gcsAndHistoryName`() {
+        // given
+        LocalGcs.uploadFileForTest("../test_projects/android/apks/app-debug.apk")
+        LocalGcs.uploadFileForTest("../test_projects/android/apks/app-debug-androidTest.apk")
+
+        // then
         val gcsConfig = AndroidArgs.load(Paths.get("src/test/kotlin/ftl/fixtures/flank.gcs.yml"))
         runBlocking {
             gcsConfig.newTestRun()

test_runner/src/test/kotlin/ftl/test/util/FlankTestRunner.kt

@@ -1,6 +1,9 @@
 package ftl.test.util
 
 import ftl.mock.MockServer
+import org.junit.runner.Description
+import org.junit.runner.notification.RunListener
+import org.junit.runner.notification.RunNotifier
 import org.junit.runners.BlockJUnit4ClassRunner
 
 class FlankTestRunner(klass: Class<*>) : BlockJUnit4ClassRunner(klass) {
@@ -10,7 +13,17 @@ class FlankTestRunner(klass: Class<*>) : BlockJUnit4ClassRunner(klass) {
             println("FlankTestRunner init\n")
 
             MockServer.start()
-            LocalGcs.uploadFiles()
         }
     }
+
+    override fun run(notifier: RunNotifier?) {
+        val listener = object : RunListener() {
+            override fun testFinished(description: Description?) {
+                LocalGcs.clear()
+                super.testFinished(description)
+            }
+        }
+        notifier?.addListener(listener)
+        super.run(notifier)
+    }
 }

test_runner/src/test/kotlin/ftl/test/util/LocalGcs.kt

@@ -2,6 +2,7 @@ package ftl.test.util
 
 import com.google.cloud.storage.BlobInfo
 import ftl.gc.GcStorage
+import ftl.gc.TestStorageProvider
 import ftl.run.exception.FlankGeneralError
 import org.junit.Assert
 import java.nio.file.Files
@@ -29,14 +30,9 @@ object LocalGcs {
         )
     }
 
-    fun uploadFiles() {
-        val appApk = "../test_projects/android/apks/app-debug.apk"
-        val testApk = "../test_projects/android/apks/app-debug-androidTest.apk"
-        val ipaZip = "./src/test/kotlin/ftl/fixtures/tmp/ios/EarlGreyExample/EarlGreyExample.zip"
-        val xctestrun = "./src/test/kotlin/ftl/fixtures/tmp/ios/EarlGreyExample/EarlGreyExampleSwiftTests.xctestrun"
+    fun uploadFileForTest(path: String) = uploadToMockGcs(Paths.get(path))
 
-        listOf(appApk, testApk, ipaZip, xctestrun).forEach { file ->
-            uploadToMockGcs(Paths.get(file))
-        }
+    fun clear() {
+        TestStorageProvider.clearStorage()
     }
 }