Android Base64 encode and decode return null in Unit Test

问题

I am attempting to decode a Base64 encoded string in Android using the http://developer.android.com/reference/android/util/Base64.html class.

Both the encodeToString and decode methods are returning null, and I have no idea what's wrong, here's my code for the decode:

// Should decode to "GRC"
String friendlyNameBase64Encoded = "R1JD";

// This returns null
byte[] friendlyNameByteArray = Base64.decode(friendlyNameBase64Encoded, Base64.DEFAULT);

// Fails with NullPointerException
String friendlyName = new String(friendlyNameByteArray, "UTF-8");

I'm running Android API 23.1.0

回答1:

I had the same problem in my unit tests. I didn't realize the Base64 class I'm using is a part of the Android API, therefore

You can't use android.util.Base64 in a regular JUnit test, it must be an Instrumentation test.

However, if you really want it as a unit test, you could use the Apache Commons Base64 class instead. Include it in Gradle build:

// https://mvnrepository.com/artifact/org.apache.commons/commons-collections4
compile group: 'org.apache.commons', name: 'commons-collections4', version: '4.1'

And then slightly different usage,

• Base64.encodeBase64String(byte[] binaryData)

• Base64.decodeBase64(String base64String)

回答2:

Follow up o android tutorials and unit test notes while you need just Unit tests without use of some android libs

In your case you're depending on android.Base64. I had similar issue and moving test classes from src/test -> src/androidTest worked. Those tests are run on virtual machine or real android device. I didn't notice the diff at the first look.

回答3:

You can use the Robolectric Runner

1. Add the dependency in your build.gradle:

   testCompile 'org.robolectric:robolectric:X.X.X'
   

2. Add this line in your testing class:

   import org.junit.runner.RunWith;
   import org.robolectric.RobolectricTestRunner;
   
   @RunWith(RobolectricTestRunner.class)
   public class MyTestingClassTest {
       ...
   }
   

回答4:

As discussed, android.util.Base64.decode is returning a null in test harness because of this setting in the build file:

testOptions {
    unitTests.returnDefaultValues = true
}

To avoid including other libraries you could fall back on java.util.Base64, which is only available in Java8 and on Android 26 and above. If you already target 26+ then just switch to this method, but if you have to target earlier SDKs you could check for the null return and call a test-harness method instead:

// Required because Android classes return null in desktop unit tests
@TargetApi(26)
private fun testHarnessDecode(s : String) : ByteArray {
    return java.util.Base64.getDecoder().decode(s)
}

I would rather do this than pull in additional library dependencies, but YMMV.

来源：https://stackoverflow.com/questions/33847781/android-base64-encode-and-decode-return-null-in-unit-test