Add isInitialized visible for testing method

library/src/main/java/com/bumptech/glide/Glide.java

@@ -183,6 +183,11 @@ public static void init(@NonNull Context context, @NonNull GlideBuilder builder)
     }
   }
 
+  @VisibleForTesting
+  public static synchronized boolean isInitialized() {
+    return glide != null;
+  }
+
   /**
    * Allows hardware Bitmaps to be used prior to the first frame in the app being drawn as soon as
    * this method is called.

library/test/src/test/java/com/bumptech/glide/InitializeGlideTest.java

@@ -1,5 +1,6 @@
 package com.bumptech.glide;
 
+import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertThrows;
 
 import android.content.Context;
@@ -69,4 +70,16 @@ public void run() throws Throwable {
     // Make sure the second exception isn't hidden by some Glide initialization related exception.
     assertThrows(TestException.class, initializeGlide);
   }
+
+  @Test
+  public void isInitialized_whenNotInitialized_returnsFalse() {
+    assertThat(Glide.isInitialized()).isFalse();
+  }
+
+  @Test
+  public void isInitialized_whenInitialized_returnsTrue() {
+    Glide.get(context);
+
+    assertThat(Glide.isInitialized()).isTrue();
+  }
 }