unit-test-writer

name	unit-test-writer
description	Use when writing or extending unit tests for Camposer — covers test infrastructure, fake classes, naming conventions, and patterns for both simple (Type A) and hardware-applied (Type B) camera properties.

Unit Tests

Camposer tests run in commonTest against fake implementations of the camera engine. No mocks, no platform hardware — all tests are hermetic and cross-platform.

Test Infrastructure

For full fake class details, file paths, and the 3-file rule see reference/FAKE_PATTERNS.md.

Class	Role
CameraSessionTest	Abstract base class — provides cameraSession, cameraTest, controller, initCameraSession(), updateSession()
FakeCameraTest	Records hardware calls and exposes assert*() helpers; configure isXxxSupported flags before initCameraSession()
FakeCameraSession	Fake session wired to FakeCameraEngine

Location: camposer/src/commonTest/kotlin/com/ujizin/camposer/session/

Imports needed:

import kotlin.test.Test
import kotlin.test.assertEquals
import kotlin.test.assertTrue
import kotlin.test.assertFalse
// for async tests only:
import kotlinx.coroutines.test.runTest

Naming Conventions

• File: CameraXxxTest.kt
• Class: internal class CameraXxxTest : CameraSessionTest()
• Methods: fun test_preview_xxx_yyy() — snake_case, describe the scenario

Type A — Simple Property (e.g. ScaleType)

Property set via updateSession(). No capability check.

internal class CameraScaleTypeTest : CameraSessionTest() {

    @Test
    fun test_preview_scale_type() {
        initCameraSession()

        ScaleType.entries.forEach { scaleType ->
            updateSession(scaleType = scaleType)

            assertEquals(scaleType, cameraSession.state.scaleType.value)
        }
    }
}

Pattern: initCameraSession() → updateSession(xxx = value) → assertEquals(state.xxx.value, value)

Type B — Hardware-Applied Property (e.g. FlashMode)

Property set via controller.setXxx(). May have a capability check (isXxxSupported).

internal class CameraFlashModeTest : CameraSessionTest() {

    @Test
    fun test_preview_all_flash_mode() {
        initCameraSession()

        FlashMode.entries.forEach { expected ->
            controller.setFlashMode(expected)

            assertFlashMode(expected)
            assertTrue(cameraSession.info.state.value.isFlashSupported)
        }
    }

    @Test
    fun test_preview_flash_mode_on_with_no_support() {
        cameraTest.isFlashSupported = false  // set BEFORE initCameraSession()

        initCameraSession()

        val result = controller.setFlashMode(FlashMode.On)

        assertTrue(result.isFailure)
        assertFalse(cameraSession.info.state.value.isFlashSupported)
        assertFlashMode(FlashMode.Off)  // state unchanged
    }

    private fun assertFlashMode(expected: FlashMode) {
        cameraTest.assertFlashMode(expected)                    // fake recorded it
        assertEquals(expected, cameraSession.state.flashMode.value)  // state matches
    }
}

Pattern: initCameraSession() → controller.setXxx(value) → cameraTest.assertXxx(value) + assertEquals(state.xxx.value, value)

Capability-unsupported pattern: set cameraTest.isXxxSupported = false → initCameraSession() → controller.setXxx(...) → assertTrue(result.isFailure) → assert state unchanged.

Async Tests (e.g. Zoom)

Wrap in runTest when the property flows through coroutines:

@Test
fun test_preview_zoom_change() = runTest {
    initCameraSession()

    val expected = 4F
    cameraSession.controller.setZoomRatio(expected)

    cameraTest.assertZoomRatio(expected)
    assertEquals(expected, cameraSession.state.zoomRatio.value)
}

Required Test Cases

For every new property, cover:

1. Happy path — each enum value (or representative values) applied correctly
2. Unsupported capability — result.isFailure, state unchanged (Type B with capability check only)
3. Boundary values — min/max for numeric properties (zoom, exposure)

Common Mistakes

Mistake	Fix
Setting cameraTest.isXxxSupported after initCameraSession()	Must be set BEFORE — fake reads flags at init
Asserting only cameraSession.state without cameraTest.assertXxx()	Always assert both — state and fake recording
Using runTest for sync property tests	Only needed for properties that emit through coroutine flows asynchronously
Checking state before calling controller.setXxx()	Call the setter first, then assert