Create a Promise class to simplify dealing with async results.

base/android/junit/src/org/chromium/base/PromiseTest.java

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.base;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.chromium.base.Promise.UnhandledRejectionException;
+import org.chromium.testing.local.LocalRobolectricTestRunner;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.annotation.Config;
+import org.robolectric.shadows.ShadowHandler;
+
+/** Unit tests for {@link Promise}. */
+@RunWith(LocalRobolectricTestRunner.class)
+@Config(manifest = Config.NONE)
+public class PromiseTest {
+    // We need a simple mutable reference type for testing.
+    private static class Value {
+        private int mValue;
+
+        public int get() {
+            return mValue;
+        }
+
+        public void set(int value) {
+            mValue = value;
+        }
+    }
+
+    /** Tests that the callback is called on fulfillment. */
+    @Test
+    public void callback() {
+        final Value value = new Value();
+
+        Promise<Integer> promise = new Promise<Integer>();
+        promise.then(this.<Integer>setValue(value, 1));
+
+        assertEquals(value.get(), 0);
+
+        promise.fulfill(new Integer(1));
+        assertEquals(value.get(), 1);
+    }
+
+    /** Tests that multiple callbacks are called. */
+    @Test
+    public void multipleCallbacks() {
+        final Value value = new Value();
+
+        Promise<Integer> promise = new Promise<Integer>();
+        Callback<Integer> callback = new Callback<Integer>() {
+            @Override
+            public void onResult(Integer result) {
+                value.set(value.get() + 1);
+            }
+        };
+        promise.then(callback);
+        promise.then(callback);
+
+        assertEquals(value.get(), 0);
+
+        promise.fulfill(new Integer(0));
+        assertEquals(value.get(), 2);
+    }
+
+    /** Tests that a callback is called immediately when given to a fulfilled Promise. */
+    @Test
+    public void callbackOnFulfilled() {
+        final Value value = new Value();
+
+        Promise<Integer> promise = Promise.fulfilled(new Integer(0));
+        assertEquals(value.get(), 0);
+
+        promise.then(this.<Integer>setValue(value, 1));
+
+        assertEquals(value.get(), 1);
+    }
+
+    /** Tests that promises can chain synchronous functions correctly. */
+    @Test
+    public void promiseChaining() {
+        Promise<Integer> promise = new Promise<Integer>();
+        final Value value = new Value();
+
+        promise.then(new Promise.Function<Integer, String>(){
+                    @Override
+                    public String apply(Integer arg) {
+                        return arg.toString();
+                    }
+                }).then(new Promise.Function<String, String>(){
+                    @Override
+                    public String apply(String arg) {
+                        return arg + arg;
+                    }
+                }).then(new Callback<String>() {
+                    @Override
+                    public void onResult(String result) {
+                        value.set(result.length());
+                    }
+                });
+
+        promise.fulfill(new Integer(123));
+        ShadowHandler.runMainLooperToEndOfTasks();
+        assertEquals(6, value.get());
+    }
+
+    /** Tests that promises can chain asynchronous functions correctly. */
+    @Test
+    public void promiseChainingAsyncFunctions() {
+        Promise<Integer> promise = new Promise<Integer>();
+        final Value value = new Value();
+
+        final Promise<String> innerPromise = new Promise<String>();
+
+        promise.then(new Promise.AsyncFunction<Integer, String>() {
+                    @Override
+                    public Promise<String> apply(Integer arg) {
+                        return innerPromise;
+                    }
+                }).then(new Callback<String>(){
+                    @Override
+                    public void onResult(String result) {
+                        value.set(result.length());
+                    }
+                });
+
+        assertEquals(0, value.get());
+
+        promise.fulfill(5);
+        ShadowHandler.runMainLooperToEndOfTasks();
+        assertEquals(0, value.get());
+
+        innerPromise.fulfill("abc");
+        ShadowHandler.runMainLooperToEndOfTasks();
+        assertEquals(3, value.get());
+    }
+
+    /** Tests that a Promise that does not use its result does not throw on rejection. */
+    @Test
+    public void rejectPromiseNoCallbacks() {
+        Promise<Integer> promise = new Promise<Integer>();
+
+        boolean caught = false;
+        try {
+            promise.reject();
+            ShadowHandler.runMainLooperToEndOfTasks();
+        } catch (UnhandledRejectionException e) {
+            caught = true;
+        }
+        assertFalse(caught);
+    }
+
+    /** Tests that a Promise that uses its result throws on rejection if it has no handler. */
+    @Test
+    public void rejectPromiseNoHandler() {
+        Promise<Integer> promise = new Promise<Integer>();
+        promise.then(this.<Integer>identity()).then(this.<Integer>pass());
+
+        boolean caught = false;
+        try {
+            promise.reject();
+            ShadowHandler.runMainLooperToEndOfTasks();
+        } catch (UnhandledRejectionException e) {
+            caught = true;
+        }
+        assertTrue(caught);
+    }
+
+    /** Tests that a Promise that handles rejection does not throw on rejection. */
+    @Test
+    public void rejectPromiseHandled() {
+        Promise<Integer> promise = new Promise<Integer>();
+        promise.then(this.<Integer>identity()).then(this.<Integer>pass(), this.<Exception>pass());
+
+        boolean caught = false;
+        try {
+            promise.reject();
+            ShadowHandler.runMainLooperToEndOfTasks();
+        } catch (UnhandledRejectionException e) {
+            caught = true;
+        }
+        assertFalse(caught);
+    }
+
+    /** Tests that rejections carry the exception information. */
+    @Test
+    public void rejectionInformation() {
+        Promise<Integer> promise = new Promise<Integer>();
+        promise.then(this.<Integer>pass());
+
+        String message = "Promise Test";
+        try {
+            promise.reject(new NegativeArraySizeException(message));
+            ShadowHandler.runMainLooperToEndOfTasks();
+        } catch (UnhandledRejectionException e) {
+            assertTrue(e.getCause() instanceof NegativeArraySizeException);
+            assertEquals(e.getCause().getMessage(), message);
+        }
+    }
+
+    /** Tests that rejections propagate. */
+    @Test
+    public void rejectionChaining() {
+        final Value value = new Value();
+        Promise<Integer> promise = new Promise<Integer>();
+
+        Promise<Integer> result =
+                promise.then(this.<Integer>identity()).then(this.<Integer>identity());
+
+        result.then(this.<Integer>pass(), this.<Exception>setValue(value, 5));
+
+        promise.reject(new Exception());
+        ShadowHandler.runMainLooperToEndOfTasks();
+
+        assertEquals(value.get(), 5);
+        assertTrue(result.isRejected());
+    }
+
+    /** Tests that Promises get rejected if a Function throws. */
+    @Test
+    public void rejectOnThrow() {
+        Value value = new Value();
+        Promise<Integer> promise = new Promise<Integer>();
+        promise.then(new Promise.Function<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer argument) {
+                throw new IllegalArgumentException();
+            }
+        }).then(this.<Integer>pass(), this.<Exception>setValue(value, 5));
+
+        promise.fulfill(0);
+
+        ShadowHandler.runMainLooperToEndOfTasks();
+        assertEquals(value.get(), 5);
+    }
+
+    /** Tests that Promises get rejected if an AsyncFunction throws. */
+    @Test
+    public void rejectOnAsyncThrow() {
+        Value value = new Value();
+        Promise<Integer> promise = new Promise<Integer>();
+
+        promise.then(new Promise.AsyncFunction<Integer, Integer>() {
+            @Override
+            public Promise<Integer> apply(Integer argument) {
+                throw new IllegalArgumentException();
+            }
+        }).then(this.<Integer>pass(), this.<Exception>setValue(value, 5));
+
+        promise.fulfill(0);
+
+        ShadowHandler.runMainLooperToEndOfTasks();
+        assertEquals(value.get(), 5);
+    }
+
+    /** Tests that Promises get rejected if an AsyncFunction rejects. */
+    @Test
+    public void rejectOnAsyncReject() {
+        Value value = new Value();
+        Promise<Integer> promise = new Promise<Integer>();
+        final Promise<Integer> inner = new Promise<Integer>();
+
+        promise.then(new Promise.AsyncFunction<Integer, Integer>() {
+            @Override
+            public Promise<Integer> apply(Integer argument) {
+                return inner;
+            }
+        }).then(this.<Integer>pass(), this.<Exception>setValue(value, 5));
+
+        promise.fulfill(0);
+
+        ShadowHandler.runMainLooperToEndOfTasks();
+        assertEquals(value.get(), 0);
+
+        inner.reject();
+
+        ShadowHandler.runMainLooperToEndOfTasks();
+        assertEquals(value.get(), 5);
+    }
+
+    /** Convenience method that returns a Callback that does nothing with its result. */
+    private static <T> Callback<T> pass() {
+        return new Callback<T>() {
+            @Override
+            public void onResult(T result) {}
+        };
+    }
+
+    /** Convenience method that returns a Function that just passes through its argument. */
+    private static <T> Promise.Function<T, T> identity() {
+        return new Promise.Function<T, T>() {
+            @Override
+            public T apply(T argument) {
+                return argument;
+            }
+        };
+    }
+
+    /** Convenience method that returns a Callback that sets the given Value on execution. */
+    private static <T> Callback<T> setValue(final Value toSet, final int value) {
+        return new Callback<T>() {
+            @Override
+            public void onResult(T result) {
+                toSet.set(value);
+            }
+        };
+    }
+}