Don't assume non-null values for any fields in testMatrix (#61)

* Don't assume non-null values for any fields in testMatrix

* adding test to cover this scenario

Author: rnakade

AndroidXCI/lib/src/main/kotlin/dev/androidx/ci/testRunner/TestExecutionStore.kt

@@ -46,10 +46,16 @@ internal class TestExecutionStore(
     suspend fun getTestExecutionSteps(
         testMatrix: TestMatrix
     ): List<Step> {
-        return getTestExecutionSteps(
-            projectId = testMatrix.projectId!!,
-            historyId = testMatrix.resultStorage.toolResultsExecution?.historyId!!,
-            executionId = testMatrix.resultStorage.toolResultsExecution.executionId!!
-        )
+        return testMatrix.projectId?.let { projectId ->
+            testMatrix.resultStorage.toolResultsExecution?.historyId?.let { historyId ->
+                testMatrix.resultStorage.toolResultsExecution.executionId?.let { executionId ->
+                    getTestExecutionSteps(
+                        projectId = projectId,
+                        historyId = historyId,
+                        executionId = executionId
+                    )
+                }
+            }
+        } ?: emptyList()
     }
 }

AndroidXCI/lib/src/test/kotlin/dev/androidx/ci/testRunner/TestExecutionStoreTest.kt

@@ -81,4 +81,24 @@ internal class TestExecutionStoreTest {
         assertThat(outputSteps).hasSize(2)
         assertThat(outputSteps).containsExactlyElementsIn(inputSteps)
     }
+
+    @Test
+    fun getExecutionStepsNullValuesForExecutionIdHistoryId() = runBlocking<Unit> {
+        val resultPath = "${fakeBackend.fakeGoogleCloudApi.rootGcsPath}/my-test-matrix-results"
+        val testMatrix = fakeBackend.fakeFirebaseTestLabApi.createTestMatrix(
+            projectId = fakeBackend.firebaseProjectId,
+            requestId = "requestId",
+            testMatrix = TestMatrix(
+                resultStorage = ResultStorage(
+                    googleCloudStorage = GoogleCloudStorage(resultPath)
+                ),
+                projectId = fakeBackend.firebaseProjectId,
+                environmentMatrix = EnvironmentMatrix(),
+                testSpecification = TestSpecification()
+            )
+        )
+
+        val outputSteps = testExecutionStore.getTestExecutionSteps(testMatrix)
+        assertThat(outputSteps).isEmpty()
+    }
 }