Use lateinit var to remove !! and created a common TestFileUtils (#11155)

### Summary
This change did two changes:
* Use lateinit var to remove !!
* Created a common TestFileUtils to share the same code for
getTestFilePath across all instrumentation test code.


### Test plan
./gradlew :executorch_android:connectedAndroidTest

Co-authored-by: Haiting Pu <[email protected]>

Author: phaiting

extension/android/executorch_android/src/androidTest/java/org/pytorch/executorch/LlmModuleInstrumentationTest.kt

@@ -18,10 +18,14 @@ import org.apache.commons.io.FileUtils
 import org.json.JSONException
 import org.json.JSONObject
 import org.junit.Assert
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertThat
+import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
+import org.pytorch.executorch.TestFileUtils.getTestFilePath
 import org.pytorch.executorch.extension.llm.LlmCallback
 import org.pytorch.executorch.extension.llm.LlmModule
 
@@ -30,7 +34,7 @@ import org.pytorch.executorch.extension.llm.LlmModule
 class LlmModuleInstrumentationTest : LlmCallback {
     private val results: MutableList<String> = ArrayList()
     private val tokensPerSecond: MutableList<Float> = ArrayList()
-    private var llmModule: LlmModule? = null
+    private lateinit var llmModule: LlmModule
 
     @Before
     @Throws(IOException::class)
@@ -57,25 +61,25 @@ class LlmModuleInstrumentationTest : LlmCallback {
     @Test
     @Throws(IOException::class, URISyntaxException::class)
     fun testGenerate() {
-        val loadResult = llmModule!!.load()
+        val loadResult = llmModule.load()
         // Check that the model can be load successfully
-        Assert.assertEquals(OK.toLong(), loadResult.toLong())
+        assertEquals(OK.toLong(), loadResult.toLong())
 
-        llmModule!!.generate(TEST_PROMPT, SEQ_LEN, this@LlmModuleInstrumentationTest)
-        Assert.assertEquals(results.size.toLong(), SEQ_LEN.toLong())
-        Assert.assertTrue(tokensPerSecond[tokensPerSecond.size - 1] > 0)
+        llmModule.generate(TEST_PROMPT, SEQ_LEN, this@LlmModuleInstrumentationTest)
+        assertEquals(results.size.toLong(), SEQ_LEN.toLong())
+        assertTrue(tokensPerSecond[tokensPerSecond.size - 1] > 0)
     }
 
     @Test
     @Throws(IOException::class, URISyntaxException::class)
     fun testGenerateAndStop() {
-        llmModule!!.generate(
+        llmModule.generate(
             TEST_PROMPT,
             SEQ_LEN,
             object : LlmCallback {
                 override fun onResult(result: String) {
                     this@LlmModuleInstrumentationTest.onResult(result)
-                    llmModule!!.stop()
+                    llmModule.stop()
                 }
 
                 override fun onStats(stats: String) {
@@ -85,7 +89,7 @@ class LlmModuleInstrumentationTest : LlmCallback {
         )
 
         val stoppedResultSize = results.size
-        Assert.assertTrue(stoppedResultSize < SEQ_LEN)
+        assertTrue(stoppedResultSize < SEQ_LEN)
     }
 
     override fun onResult(result: String) {
@@ -101,7 +105,8 @@ class LlmModuleInstrumentationTest : LlmCallback {
             val promptEvalEndMs = jsonObject.getInt("prompt_eval_end_ms")
             tps = numGeneratedTokens.toFloat() / (inferenceEndMs - promptEvalEndMs) * 1000
             tokensPerSecond.add(tps)
-        } catch (_: JSONException) {}
+        } catch (_: JSONException) {
+        }
     }
 
     companion object {
@@ -110,12 +115,5 @@ class LlmModuleInstrumentationTest : LlmCallback {
         private const val TEST_PROMPT = "Hello"
         private const val OK = 0x00
         private const val SEQ_LEN = 32
-
-        private fun getTestFilePath(fileName: String): String {
-            return InstrumentationRegistry.getInstrumentation()
-                .targetContext
-                .externalCacheDir
-                .toString() + fileName
-        }
     }
 }

extension/android/executorch_android/src/androidTest/java/org/pytorch/executorch/ModuleE2ETest.kt

@@ -22,6 +22,7 @@ import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.pytorch.executorch.TensorImageUtils.bitmapToFloat32Tensor
+import org.pytorch.executorch.TestFileUtils.getTestFilePath
 
 /** Unit tests for [Module]. */
 @RunWith(AndroidJUnit4::class)
@@ -90,12 +91,6 @@ class ModuleE2ETest {
     }
 
     companion object {
-        private fun getTestFilePath(fileName: String): String {
-            return InstrumentationRegistry.getInstrumentation()
-                .targetContext
-                .externalCacheDir
-                .toString() + fileName
-        }
 
         fun argmax(array: FloatArray): Int {
             require(array.isNotEmpty()) { "Array cannot be empty" }

extension/android/executorch_android/src/androidTest/java/org/pytorch/executorch/ModuleInstrumentationTest.kt

@@ -23,6 +23,7 @@ import org.junit.Before
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
+import org.pytorch.executorch.TestFileUtils.getTestFilePath
 
 /** Unit tests for [Module]. */
 @RunWith(AndroidJUnit4::class)
@@ -173,12 +174,5 @@ class ModuleInstrumentationTest {
         private const val INVALID_STATE = 0x2
         private const val INVALID_ARGUMENT = 0x12
         private const val ACCESS_FAILED = 0x22
-
-        private fun getTestFilePath(fileName: String): String {
-            return InstrumentationRegistry.getInstrumentation()
-                .targetContext
-                .externalCacheDir
-                .toString() + fileName
-        }
     }
 }

extension/android/executorch_android/src/androidTest/java/org/pytorch/executorch/TestFileUtils.kt

@@ -0,0 +1,16 @@
+package org.pytorch.executorch
+
+import androidx.test.InstrumentationRegistry
+
+/**
+ * Test File Utils
+ */
+object TestFileUtils {
+
+    fun getTestFilePath(fileName: String): String {
+        return InstrumentationRegistry.getInstrumentation()
+            .targetContext
+            .externalCacheDir
+            .toString() + fileName
+    }
+}