Add onChangedValue method to hook and receive each value

testing/src/main/java/com/jraska/livedata/TestObserver.java

@@ -14,7 +14,7 @@
 
 public final class TestObserver<T> implements Observer<T> {
  private final List<T> valueHistory = new ArrayList<>();
- private final List<Consumer<TestObserver<T>>> onChangedConsumers = new ArrayList<>();
+ private final List<Consumer<T>> onChangedConsumers = new ArrayList<>();
  private CountDownLatch valueLatch = new CountDownLatch(1);
 
  private TestObserver() {
@@ -25,8 +25,8 @@ public void onChanged(@Nullable T value) {
  valueHistory.add(value);
  valueLatch.countDown();
 
- for (Consumer<TestObserver<T>> consumer : onChangedConsumers) {
- consumer.accept(this);
+ for (Consumer<T> consumer : onChangedConsumers) {
+ consumer.accept(value);
  }
  }
 
@@ -167,12 +167,18 @@ public <N> TestObserver<N> map(Function<T, N> mapper) {
  newObserver.onChanged(mapper.apply(value));
  }
 
- onValueChanged(observer -> newObserver.onChanged(mapper.apply(observer.value())));
+ onValueChanged(new Map<>(newObserver, mapper));
 
  return newObserver;
  }
 
- public TestObserver<T> onValueChanged(Consumer<TestObserver<T>> onObserverValue) {
+ /**
+ * Adds a Consumer which will be triggered on each value change to allow assertion on the value.
+ *
+ * @param onObserverValue Consumer to call when new value is received
+ * @return this
+ */
+ public TestObserver<T> onValueChanged(Consumer<T> onObserverValue) {
  onChangedConsumers.add(onObserverValue);
  return this;
  }
@@ -253,4 +259,18 @@ public static <T> TestObserver<T> test(LiveData<T> liveData) {
  liveData.observeForever(observer);
  return observer;
  }
+
+ static final class Map<T, N> implements Consumer<T> {
+ private final TestObserver<N> newObserver;
+ private final Function<T, N> mapper;
+
+ Map(TestObserver<N> newObserver, Function<T, N> mapper) {
+ this.newObserver = newObserver;
+ this.mapper = mapper;
+ }
+
+ @Override public void accept(T value) {
+ newObserver.onChanged(mapper.apply(value));
+ }
+ }
 }

testing/src/test/java/com/jraska/livedata/TestObserverTest.kt

@@ -3,9 +3,11 @@ package com.jraska.livedata
 import androidx.arch.core.executor.testing.InstantTaskExecutorRule
 import androidx.lifecycle.MutableLiveData
 import org.assertj.core.api.Assertions.assertThat
+import org.junit.ComparisonFailure
 import org.junit.Rule
 import org.junit.Test
 import java.util.concurrent.TimeUnit
+import java.util.concurrent.atomic.AtomicInteger
 
 class TestObserverTest {
  @get:Rule val testRule = InstantTaskExecutorRule()
@@ -135,6 +137,22 @@ class TestObserverTest {
  testObserver.map { it.toString() }.assertValue("4")
  }
 
+ @Test
+ fun whenOnValueChanged_thenTriggersProperly() {
+ val triggeredCount = AtomicInteger()
+
+ TestObserver.test(testLiveData)
+ .map { it * 2 }
+ .onValueChanged { triggeredCount.incrementAndGet() }
+
+ val expectedTriggerCount = 10
+ repeat(expectedTriggerCount) {
+ testLiveData.value = 123456
+ }
+
+ assertThat(triggeredCount.get()).isEqualTo(expectedTriggerCount)
+ }
+
  @Test(expected = AssertionError::class)
  fun hasValuesAssertionFailsOnNoValue() {
  TestObserver.test(testLiveData).assertHasValue()
@@ -178,6 +196,15 @@ class TestObserverTest {
  testObserver.assertNever { it == 4 }
  }
 
+ @Test(expected = ComparisonFailure::class)
+ fun whenOnValueChanged_thenFailsProperly() {
+ TestObserver.test(testLiveData)
+ .map { it * 2 }
+ .onValueChanged { assertThat(it).isEqualTo(1) }
+
+ testLiveData.value = 1
+ }
+
  private fun setValueAsOne() = Runnable {
  Thread.sleep(10)
  testLiveData.value = 1