Stop swallowing coroutine errors nobody asserted on

`drainEscapedCoroutineErrors()` cleared the collector at rule-construction time
with `runCatching { runTest {} }`, and discarding what it found was the whole
mechanism: it could not tell the one known deposit from an escaped error nobody
had asserted on. That traded a loud, misleading failure for a silent one, which
was acceptable only while exactly one depositor existed and the seam to remove it
did not.

The seam exists now, so the depositor is gone: the OOM is consumed by the test
that raises it. Every Compose class takes the v2 `createComposeRule()` directly,
and a future escaped error fails a test again instead of disappearing.

The two findings the drain's KDoc carried that outlive it: the v2 rule and the
non-v2 `StateRestorationTester` do interoperate -- the note now sits at the two
declarations that pair them -- and a drain could never have been a `@Before`
(the rule's `runTest` wraps it) or a `@BeforeClass` (Robolectric runs that
outside the sandbox classloader, where the collector is a different object).

Full JVM suite run twice in a row with the drain deleted: 373 tests, 0 failures
both times.

Closes #66

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/test/java/org/libremediaconverter/AppRootRestorationTest.kt

@@ -8,6 +8,7 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.platform.testTag
 import androidx.compose.ui.test.assertIsSelected
 import androidx.compose.ui.test.junit4.StateRestorationTester
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performClick
@@ -41,11 +42,11 @@ import org.robolectric.RobolectricTestRunner
 @RunWith(RobolectricTestRunner::class)
 class AppRootRestorationTest {
 
-    // Not `createComposeRule()` directly: see [drainEscapedCoroutineErrors]. Every Compose test
-    // class in this source set starts there, whether or not it is the one that happens to be
-    // running when another test's escaped coroutine error is delivered.
+    // The rule is the **v2** one (`androidx.compose.ui.test.junit4.v2`) while
+    // [StateRestorationTester], which takes it below, is not. The mismatched imports are
+    // deliberate: the v2 package has no tester of its own and the two do interoperate.
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     private val restoration = StateRestorationTester(composeRule)
 

app/src/test/java/org/libremediaconverter/EscapedCoroutineErrors.kt

@@ -1,53 +0,0 @@
-package org.libremediaconverter
-
-import androidx.compose.ui.test.junit4.v2.createComposeRule
-import kotlinx.coroutines.test.runTest
-
-/**
- * Clears coroutine errors this module's tests deliberately let escape, so they land on the test
- * that caused them instead of on the next one to start.
- *
- * **Every Compose test class in `src/test` has to start here.** `createComposeRule` runs the
- * composition inside `runTest`, and `runTest` opens by throwing `UncaughtExceptionsBeforeTest` for
- * anything already sitting in kotlinx-coroutines-test's collector -- a process-wide
- * `CoroutineExceptionHandler` it installs once and never removes.
- *
- * There is one deposit into that collector here, and it is not a mistake:
- * `ConversionViewModelProbeFailureTest.an OutOfMemoryError is not swallowed` proves an OOM raised
- * inside the probe is rethrown rather than reported as an unreadable file. `onInputPicked` runs it
- * in `viewModelScope.launch`, which has no exception handler by design -- the ViewModel's own KDoc
- * says a real OOM should reach the thread's handler and take the process down. On the JVM the
- * collector takes it instead, holds it, and hands it to whichever `runTest` starts next.
- *
- * It surfaced as two *different* Compose test classes failing on two consecutive runs of the same,
- * green, code, with a message naming neither the test nor the error's origin. Which class catches
- * it moves because the throw happens on a real `Dispatchers.IO` thread, after the state assertion
- * that ends the test that caused it -- so it can be delivered long after that class is done.
- *
- * A `@Before` method cannot do this: the compose rule's `runTest` wraps the statement that calls
- * `@Before`, so it has already thrown. `@BeforeClass` cannot either -- Robolectric runs it outside
- * the sandbox classloader, where the collector is a different object. Draining while the rule is
- * being *constructed* is early enough, because JUnit builds a fresh test-class instance, and with
- * it every `@get:Rule` field, before evaluating any rule.
- *
- * The real fix is a seam: give the probe hop an injectable dispatcher the way
- * `ConversionViewModel`'s constructor already does for `cleanupDispatcher`, and the error would
- * have somewhere to land. That is a production change, so it belongs in its own commit.
- */
-fun drainEscapedCoroutineErrors() {
-    // Entering a test scope is what flushes the collector; the flush is reported as this
-    // throwing, and there is nothing to assert about an error another test already asserted on.
-    runCatching { runTest {} }
-}
-
-/**
- * [createComposeRule], with [drainEscapedCoroutineErrors] run first. Use this rather than
- * `createComposeRule` directly in `src/test`.
- *
- * It also keeps the one mixed import in one place: the rule comes from the **v2** package
- * (`androidx.compose.ui.test.junit4.v2`) while `StateRestorationTester`, which takes it, does not.
- */
-fun createDrainedComposeRule() = run {
-    drainEscapedCoroutineErrors()
-    createComposeRule()
-}

app/src/test/java/org/libremediaconverter/convert/AdvancedPanelSavedStateTest.kt

@@ -7,6 +7,7 @@ import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.MutableState
 import androidx.compose.runtime.saveable.LocalSaveableStateRegistry
 import androidx.compose.runtime.saveable.SaveableStateRegistry
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.performClick
 import androidx.media3.common.util.UnstableApi
@@ -15,7 +16,6 @@ import org.junit.Assert.assertTrue
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.AudioCodec
 import org.libremediaconverter.model.Container
 import org.libremediaconverter.model.OutputSpec
@@ -57,9 +57,8 @@ import org.robolectric.RobolectricTestRunner
 @RunWith(RobolectricTestRunner::class)
 class AdvancedPanelSavedStateTest {
 
-    // Not `createComposeRule()` directly: see [drainEscapedCoroutineErrors].
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     /**
      * `canBeSaved = { true }` deliberately.

app/src/test/java/org/libremediaconverter/convert/AdvancedPickerTest.kt

@@ -6,6 +6,7 @@ import androidx.compose.ui.test.hasAnyAncestor
 import androidx.compose.ui.test.hasTestTag
 import androidx.compose.ui.test.hasText
 import androidx.compose.ui.test.junit4.StateRestorationTester
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onAllNodesWithTag
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.onNodeWithText
@@ -16,7 +17,6 @@ import org.junit.Assert.assertTrue
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.AudioCodec
 import org.libremediaconverter.model.Container
 import org.libremediaconverter.model.ContainerCapabilities
@@ -61,9 +61,11 @@ import org.robolectric.RobolectricTestRunner
 @RunWith(RobolectricTestRunner::class)
 class AdvancedPickerTest {
 
-    // Not `createComposeRule()` directly: see [drainEscapedCoroutineErrors].
+    // The rule is the **v2** one (`androidx.compose.ui.test.junit4.v2`) while
+    // [StateRestorationTester], which takes it below, is not. The mismatched imports are
+    // deliberate: the v2 package has no tester of its own and the two do interoperate.
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     private val restoration = StateRestorationTester(composeRule)
 

app/src/test/java/org/libremediaconverter/convert/ConverterLeafTagsTest.kt

@@ -2,6 +2,7 @@ package org.libremediaconverter.convert
 
 import android.net.Uri
 import androidx.compose.ui.test.assertCountEquals
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onAllNodesWithTag
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.performClick
@@ -9,7 +10,6 @@ import androidx.media3.common.util.UnstableApi
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.AudioCodec
 import org.libremediaconverter.model.Container
 import org.libremediaconverter.model.EnginePreference
@@ -47,7 +47,7 @@ import org.robolectric.RobolectricTestRunner
 class ConverterLeafTagsTest {
 
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     private fun assertResolvesToOneNode(tag: String) {
         composeRule.onAllNodesWithTag(tag).assertCountEquals(1)

app/src/test/java/org/libremediaconverter/convert/ConverterPickerSelectionTest.kt

@@ -6,6 +6,7 @@ import androidx.compose.ui.test.assertIsSelected
 import androidx.compose.ui.test.hasAnyAncestor
 import androidx.compose.ui.test.hasTestTag
 import androidx.compose.ui.test.hasText
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performClick
 import androidx.media3.common.util.UnstableApi
@@ -13,7 +14,6 @@ import org.junit.Assert.assertEquals
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.EnginePreference
 import org.libremediaconverter.model.OutputFormat
 import org.libremediaconverter.model.QualityTier
@@ -48,7 +48,7 @@ import org.robolectric.RobolectricTestRunner
 class ConverterPickerSelectionTest {
 
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     /**
      * The chip carrying [label] inside the row tagged [rowTag].

app/src/test/java/org/libremediaconverter/convert/ConverterScreenContentTest.kt

@@ -1,6 +1,7 @@
 package org.libremediaconverter.convert
 
 import android.net.Uri
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.performClick
 import androidx.compose.ui.test.performScrollTo
@@ -9,7 +10,6 @@ import org.junit.Assert.assertEquals
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.Validation
 import org.libremediaconverter.ui.TestTags
 import org.robolectric.RobolectricTestRunner
@@ -39,9 +39,8 @@ import java.io.File
 @RunWith(RobolectricTestRunner::class)
 class ConverterScreenContentTest {
 
-    // Not `createComposeRule()` directly: see [org.libremediaconverter.drainEscapedCoroutineErrors].
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     /** What the screen asked to save, in the order it asked. Empty until Save is tapped. */
     private val savedAs = mutableListOf<String>()

app/src/test/java/org/libremediaconverter/convert/ConverterStateAffordancesTest.kt

@@ -6,6 +6,7 @@ import androidx.compose.ui.test.assertIsEnabled
 import androidx.compose.ui.test.assertIsNotEnabled
 import androidx.compose.ui.test.assertRangeInfoEquals
 import androidx.compose.ui.test.assertTextEquals
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performClick
@@ -15,7 +16,6 @@ import org.junit.Assert.assertEquals
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.AudioCodec
 import org.libremediaconverter.model.Container
 import org.libremediaconverter.model.OutputSpec
@@ -72,9 +72,8 @@ import java.io.File
 @RunWith(RobolectricTestRunner::class)
 class ConverterStateAffordancesTest {
 
-    // Not `createComposeRule()` directly: see [org.libremediaconverter.drainEscapedCoroutineErrors].
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     /**
      * Every callback the screen fired, in order, tagged with the value it carried.

app/src/test/java/org/libremediaconverter/convert/FileCardTest.kt

@@ -3,13 +3,13 @@ package org.libremediaconverter.convert
 import android.net.Uri
 import androidx.compose.ui.test.assertCountEquals
 import androidx.compose.ui.test.assertTextEquals
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onChildren
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.media3.common.util.UnstableApi
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.AudioCodec
 import org.libremediaconverter.model.Container
 import org.libremediaconverter.model.InputKind
@@ -56,7 +56,7 @@ import org.robolectric.RobolectricTestRunner
 class FileCardTest {
 
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     @Test
     fun `a file no provider could measure says so in words rather than showing a zero`() {

app/src/test/java/org/libremediaconverter/join/JoinLeafTagsTest.kt

@@ -2,13 +2,13 @@ package org.libremediaconverter.join
 
 import android.net.Uri
 import androidx.compose.ui.test.assertCountEquals
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onAllNodesWithTag
 import androidx.media3.common.util.UnstableApi
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.libremediaconverter.convert.InputFile
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.ui.TestTags
 import org.robolectric.RobolectricTestRunner
 
@@ -32,7 +32,7 @@ import org.robolectric.RobolectricTestRunner
 class JoinLeafTagsTest {
 
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     private fun input(displayName: String) = InputFile(
         uri = Uri.parse("content://test/$displayName"),

app/src/test/java/org/libremediaconverter/join/JoinScreenContentTest.kt

@@ -1,5 +1,6 @@
 package org.libremediaconverter.join
 
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.performClick
 import androidx.compose.ui.test.performScrollTo
@@ -8,7 +9,6 @@ import org.junit.Assert.assertEquals
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.ConcatStrategy
 import org.libremediaconverter.ui.TestTags
 import org.robolectric.RobolectricTestRunner
@@ -35,9 +35,8 @@ import java.io.File
 @RunWith(RobolectricTestRunner::class)
 class JoinScreenContentTest {
 
-    // Not `createComposeRule()` directly: see [org.libremediaconverter.drainEscapedCoroutineErrors].
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     /** What the screen asked to save, in the order it asked. Empty until Save is tapped. */
     private val savedAs = mutableListOf<String>()

app/src/test/java/org/libremediaconverter/join/JoinStateAffordancesTest.kt

@@ -7,6 +7,7 @@ import androidx.compose.ui.semantics.getOrNull
 import androidx.compose.ui.test.SemanticsMatcher
 import androidx.compose.ui.test.assertRangeInfoEquals
 import androidx.compose.ui.test.assertTextEquals
+import androidx.compose.ui.test.junit4.v2.createComposeRule
 import androidx.compose.ui.test.onNodeWithTag
 import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performClick
@@ -17,7 +18,6 @@ import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.libremediaconverter.convert.InputFile
-import org.libremediaconverter.createDrainedComposeRule
 import org.libremediaconverter.model.ConcatStrategy
 import org.libremediaconverter.ui.TestTags
 import org.robolectric.RobolectricTestRunner
@@ -60,9 +60,8 @@ import java.io.File
 @RunWith(RobolectricTestRunner::class)
 class JoinStateAffordancesTest {
 
-    // Not `createComposeRule()` directly: see [org.libremediaconverter.drainEscapedCoroutineErrors].
     @get:Rule
-    val composeRule = createDrainedComposeRule()
+    val composeRule = createComposeRule()
 
     /** Which callback the screen invoked, in order, with what it passed. Empty until one fires. */
     private val events = mutableListOf<String>()