Adding simple unit tests

.travis.yml

@@ -18,4 +18,5 @@ before_install:
 install:
   - ./gradlew
 script:
-  - ./gradlew assembleDebug --stacktrace
+  - ./gradlew :app:assembleDebug --stacktrace
+  - ./gradlew :app:test --stacktrace

app/build.gradle

@@ -63,6 +63,7 @@ dexcount {
 }
 
 dependencies {
+    testCompile 'junit:junit:4.12'
 
     // support libraries
     def supportLibVersion = '25.4.0'

app/src/test/java/acr/browser/lightning/utils/PreconditionsTest.java

@@ -0,0 +1,19 @@
+package acr.browser.lightning.utils;
+
+import org.junit.Test;
+
+/**
+ * Unit tests for {@link Preconditions}.
+ */
+public class PreconditionsTest {
+
+    @Test(expected = RuntimeException.class)
+    public void checkNonNull_Null_ThrowsException() {
+        Preconditions.checkNonNull(null);
+    }
+
+    @Test
+    public void checkNonNull_NonNull_Succeeds() {
+        Preconditions.checkNonNull(new Object());
+    }
+}

app/src/test/java/acr/browser/lightning/utils/SubscriptionUtilsTest.java

@@ -0,0 +1,41 @@
+package acr.browser.lightning.utils;
+
+import com.anthonycr.bonsai.Subscription;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit tests for {@link SubscriptionUtils}.
+ */
+public class SubscriptionUtilsTest {
+
+    @Test
+    public void safeUnsubscribe_NullSubscription_Succeeds() {
+        SubscriptionUtils.safeUnsubscribe(null);
+    }
+
+    @Test
+    public void safeUnsubscribe_NonNullSubscription_SuccessfullyUnsubscribes() {
+        Subscription subscription = new Subscription() {
+
+            boolean isUnsubscribed = false;
+
+            @Override
+            public void unsubscribe() {
+                isUnsubscribed = true;
+            }
+
+            @Override
+            public boolean isUnsubscribed() {
+                return isUnsubscribed;
+            }
+        };
+
+        Assert.assertFalse(subscription.isUnsubscribed());
+
+        SubscriptionUtils.safeUnsubscribe(subscription);
+
+        Assert.assertTrue(subscription.isUnsubscribed());
+    }
+}