make some better use of mocks during unit tests

main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/Aes256Cryptor.java

@@ -103,14 +103,11 @@ public class Aes256Cryptor implements Cryptor, AesCryptographicConfiguration {
 	/**
 	 * Creates a new Cryptor with a newly initialized PRNG.
 	 */
-	public Aes256Cryptor() {
-		try {
-			securePrng = SecureRandom.getInstanceStrong();
-			// No setSeed needed. See SecureRandom.getInstance(String):
-			// The first call to nextBytes will force the SecureRandom object to seed itself
-		} catch (NoSuchAlgorithmException e) {
-			throw new IllegalStateException("PRNG algorithm should exist.", e);
-		}
+
+	Aes256Cryptor(SecureRandom securePrng) {
+		this.securePrng = securePrng;
+		// No setSeed needed. See SecureRandom.getInstance(String):
+		// The first call to nextBytes will force the SecureRandom object to seed itself
 	}
 
 	@Override

main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/CryptoComponent.java

@@ -0,0 +1,15 @@
+package org.cryptomator.crypto.aes256;
+
+import javax.inject.Singleton;
+
+import org.cryptomator.crypto.Cryptor;
+
+import dagger.Component;
+
+@Singleton
+@Component(modules = CryptoModule.class)
+interface CryptoComponent {
+
+	Cryptor cryptor();
+
+}

main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/CryptoModule.java

@@ -0,0 +1,29 @@
+package org.cryptomator.crypto.aes256;
+
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
+
+import org.cryptomator.crypto.Cryptor;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class CryptoModule {
+
+	@Provides
+	SecureRandom provideRandomNumberGenerator() {
+		try {
+			return SecureRandom.getInstanceStrong();
+		} catch (NoSuchAlgorithmException e) {
+			// quote "Every implementation of the Java platform is required to support at least one strong SecureRandom implementation."
+			throw new AssertionError("No SecureRandom implementation available.");
+		}
+	}
+
+	@Provides
+	public Cryptor provideCryptor(SecureRandom secureRandom) {
+		return new Aes256Cryptor(secureRandom);
+	}
+
+}

main/crypto-aes/src/test/java/org/cryptomator/crypto/aes256/Aes256CryptorTest.java

@@ -19,6 +19,7 @@ import java.util.Arrays;
 import javax.security.auth.DestroyFailedException;
 
 import org.apache.commons.io.IOUtils;
+import org.cryptomator.crypto.Cryptor;
 import org.cryptomator.crypto.exceptions.DecryptFailedException;
 import org.cryptomator.crypto.exceptions.EncryptFailedException;
 import org.cryptomator.crypto.exceptions.UnsupportedKeyLengthException;
@@ -29,13 +30,18 @@ import org.junit.Test;
 
 public class Aes256CryptorTest {
 
-	private final Aes256Cryptor cryptor;
+	private final Cryptor cryptor;
 
 	public Aes256CryptorTest() {
-		cryptor = new Aes256Cryptor();
+		cryptor = DaggerCryptoTestComponent.create().cryptor();
 		cryptor.randomizeMasterKey();
 	}
 
+	@Test
+	public void testMultipleCryptorInstances() {
+		Assert.assertNotSame(DaggerCryptoTestComponent.create().cryptor(), DaggerCryptoTestComponent.create().cryptor());
+	}
+
 	@Test(timeout = 10000)
 	public void testCorrectPassword() throws IOException, WrongPasswordException, DecryptFailedException, UnsupportedKeyLengthException, DestroyFailedException, UnsupportedVaultException {
 		final String pw = "asd";
@@ -44,7 +50,7 @@ public class Aes256CryptorTest {
 		cryptor.encryptMasterKey(out, pw);
 		cryptor.destroy();
 
-		final Aes256Cryptor decryptor = new Aes256Cryptor();
+		final Cryptor decryptor = DaggerCryptoTestComponent.create().cryptor();
 		final InputStream in = new ByteArrayInputStream(out.toByteArray());
 		decryptor.decryptMasterKey(in, pw);
 
@@ -63,7 +69,7 @@ public class Aes256CryptorTest {
 
 		// all these passwords are expected to fail.
 		final String[] wrongPws = {"a", "as", "asdf", "sdf", "das", "dsa", "foo", "bar", "baz"};
-		final Aes256Cryptor decryptor = new Aes256Cryptor();
+		final Cryptor decryptor = DaggerCryptoTestComponent.create().cryptor();
 		for (final String wrongPw : wrongPws) {
 			final InputStream in = new ByteArrayInputStream(out.toByteArray());
 			try {

main/crypto-aes/src/test/java/org/cryptomator/crypto/aes256/CryptoTestComponent.java

@@ -0,0 +1,15 @@
+package org.cryptomator.crypto.aes256;
+
+import javax.inject.Singleton;
+
+import org.cryptomator.crypto.Cryptor;
+
+import dagger.Component;
+
+@Singleton
+@Component(modules = CryptoTestModule.class)
+public interface CryptoTestComponent {
+
+	Cryptor cryptor();
+
+}

main/crypto-aes/src/test/java/org/cryptomator/crypto/aes256/CryptoTestModule.java

@@ -0,0 +1,25 @@
+package org.cryptomator.crypto.aes256;
+
+import java.security.SecureRandom;
+
+import org.cryptomator.crypto.Cryptor;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class CryptoTestModule {
+
+	@Provides
+	@SuppressWarnings("deprecation")
+	SecureRandom provideRandomNumberGenerator() {
+		// we use this class for testing only, as unit tests on CI servers tend to stall, if they rely on true randomness.
+		return new InsecureRandomMock();
+	}
+
+	@Provides
+	Cryptor provideCryptor(SecureRandom secureRandom) {
+		return new Aes256Cryptor(secureRandom);
+	}
+
+}

main/crypto-aes/src/test/java/org/cryptomator/crypto/aes256/InsecureRandomMock.java

@@ -0,0 +1,23 @@
+package org.cryptomator.crypto.aes256;
+
+import java.security.SecureRandom;
+import java.util.Random;
+
+/**
+ * <b>DO NOT USE</b>
+ * 
+ * This class is for testing only.
+ */
+@Deprecated // marked as deprecated and made package-private inside /src/test/java to avoid accidential use.
+class InsecureRandomMock extends SecureRandom {
+
+	private static final long serialVersionUID = 1505563778398085504L;
+	private final Random random = new Random();
+
+	@Override
+	public void nextBytes(byte[] bytes) {
+		// let the deterministic RNG do the work:
+		this.random.nextBytes(bytes);
+	}
+
+}