diff --git a/DzieCoin.iml b/DzieCoin.iml
index 23fef75..b3d20bc 100644
--- a/DzieCoin.iml
+++ b/DzieCoin.iml
@@ -14,5 +14,15 @@
     <orderEntry type="library" name="mysql.connector.java" level="project" />
     <orderEntry type="library" name="Maven: mysql:mysql-connector-java:8.0.30" level="project" />
     <orderEntry type="library" name="Maven: com.github.davidmoten:commons-csv:1.6.002" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: junit:junit:4.13.2" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.hamcrest:hamcrest-core:1.3" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.junit.jupiter:junit-jupiter:5.9.2" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.junit.jupiter:junit-jupiter-api:5.9.2" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.opentest4j:opentest4j:1.2.0" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.junit.platform:junit-platform-commons:1.9.2" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.apiguardian:apiguardian-api:1.1.2" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.junit.jupiter:junit-jupiter-params:5.9.2" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.junit.jupiter:junit-jupiter-engine:5.9.2" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.junit.platform:junit-platform-engine:1.9.2" level="project" />
   </component>
 </module>
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
index 190571a..5721e49 100644
--- a/pom.xml
+++ b/pom.xml
@@ -25,5 +25,17 @@
             <artifactId>commons-csv</artifactId>
             <version>1.6.002</version>
         </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>RELEASE</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>RELEASE</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 </project>
\ No newline at end of file
diff --git a/src/main/java/pl/mikorosa/dziecoin/NFT.java b/src/main/java/pl/mikorosa/dziecoin/NFT.java
index 0e161b8..9c0904e 100644
--- a/src/main/java/pl/mikorosa/dziecoin/NFT.java
+++ b/src/main/java/pl/mikorosa/dziecoin/NFT.java
@@ -21,7 +21,7 @@ public class NFT extends BlockData {
     public String getContract() {
         return contract;
     }
-    
+
     public String getData() {
         return data;
     }
diff --git a/src/test/java/pl/mikorosa/dziecoin/BlockTest.java b/src/test/java/pl/mikorosa/dziecoin/BlockTest.java
new file mode 100644
index 0000000..c7eb271
--- /dev/null
+++ b/src/test/java/pl/mikorosa/dziecoin/BlockTest.java
@@ -0,0 +1,58 @@
+package pl.mikorosa.dziecoin;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class BlockTest {
+    @Test
+    void mineBlock() {
+        Main.difficulty = 4;
+
+        List<Transaction> transactions = new ArrayList<>();
+        transactions.add(new Transaction("1", "2", 1));
+
+        Block block = new Block("0", 1, transactions);
+        block.mineBlock();
+
+        assertEquals(168149, block.getNonce());
+        assertEquals("0000e4942b486fa4779fadc32a1d0dd483e117aa57bc84f6ff5912f9abefef0e", block.getHash());
+    }
+
+    @Test
+    void alterBlock() {
+        Main.difficulty = 2;
+
+        List<Transaction> transactions = new ArrayList<>();
+        transactions.add(new Transaction("1", "2", 1));
+
+        Block block = new Block("0", 1, transactions);
+        block.mineBlock();
+
+        block.getTransactions().add(new Transaction("2", "1", 1));
+
+        Block.VerifyCodes status = block.verifyBlock();
+
+        assertEquals(Block.VerifyCodes.INVALID_BLOCK_HASH, status);
+    }
+
+    @Test
+    void invalidProofOfWork() {
+        Main.difficulty = 2;
+
+        List<Transaction> transactions = new ArrayList<>();
+        transactions.add(new Transaction("1", "2", 1));
+
+        Block block = new Block("0", 1, transactions);
+        block.mineBlock();
+
+        Main.difficulty = 4;
+
+        Block.VerifyCodes status = block.verifyBlock();
+
+        assertEquals(Block.VerifyCodes.INVALID_POW_SIGNATURE, status);
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/pl/mikorosa/dziecoin/BlockchainTest.java b/src/test/java/pl/mikorosa/dziecoin/BlockchainTest.java
new file mode 100644
index 0000000..f719966
--- /dev/null
+++ b/src/test/java/pl/mikorosa/dziecoin/BlockchainTest.java
@@ -0,0 +1,105 @@
+package pl.mikorosa.dziecoin;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class BlockchainTest {
+    @Test
+    void blockchainIntegrity() {
+        Main.difficulty = 2;
+        Blockchain b = new Blockchain("1", false);
+
+        List<Transaction> transactions1 = new ArrayList<>();
+        transactions1.add(new Transaction("1", "2", 1));
+
+        Block block1 = new Block(b.getLatestBlock().getHash(), 2, transactions1);
+        block1.mineBlock();
+
+        try {
+            b.addBlock(block1);
+        } catch(BlockchainIntegrityException e) {
+            e.printStackTrace();
+            fail();
+        }
+
+        List<Transaction> transactions2 = new ArrayList<>();
+        transactions2.add(new Transaction("2", "3", 1));
+
+        Block block2 = new Block(block1.getHash(), 3, transactions2);
+        block2.mineBlock();
+
+        try {
+            b.addBlock(block2);
+        } catch (BlockchainIntegrityException e) {
+            fail();
+        }
+    }
+
+    @Test
+    void blockchainVerify() {
+        Main.difficulty = 2;
+        Blockchain b = new Blockchain("1", false);
+
+        List<Transaction> transactions1 = new ArrayList<>();
+        transactions1.add(new Transaction("1", "2", 1));
+
+        Block block1 = new Block(b.getLatestBlock().getHash(), 2, transactions1);
+        block1.mineBlock();
+
+        try {
+            b.addBlock(block1);
+        } catch(BlockchainIntegrityException e) {
+            e.printStackTrace();
+            fail();
+        }
+
+        List<Transaction> transactions2 = new ArrayList<>();
+        transactions2.add(new Transaction("2", "3", 1));
+
+        Block block2 = new Block(block1.getHash(), 3, transactions2);
+        block2.mineBlock();
+
+        try {
+            b.addBlock(block2);
+        } catch (BlockchainIntegrityException e) {
+            fail();
+        }
+
+        assertTrue(b.validateChain() == Block.VerifyCodes.SUCCESS);
+    }
+
+    @Test
+    void blockchainIntegrityExceptionThrown() {
+        Main.difficulty = 2;
+        Blockchain b = new Blockchain("1", false);
+
+        List<Transaction> transactions1 = new ArrayList<>();
+        transactions1.add(new Transaction("1", "2", 1));
+
+        Block block1 = new Block(b.getLatestBlock().getHash(), 2, transactions1);
+        block1.mineBlock();
+
+        try {
+            b.addBlock(block1);
+        } catch(BlockchainIntegrityException e) {
+            e.printStackTrace();
+            fail();
+        }
+
+        List<Transaction> transactions2 = new ArrayList<>();
+        transactions2.add(new Transaction("2", "3", 1));
+
+        Block block2 = new Block("asdf", 3, transactions2);
+        block2.mineBlock();
+
+        try {
+            b.addBlock(block2);
+        } catch (BlockchainIntegrityException e) {
+            return; // pass
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/pl/mikorosa/dziecoin/CalculateHashTest.java b/src/test/java/pl/mikorosa/dziecoin/CalculateHashTest.java
new file mode 100644
index 0000000..4c1a4ae
--- /dev/null
+++ b/src/test/java/pl/mikorosa/dziecoin/CalculateHashTest.java
@@ -0,0 +1,18 @@
+package pl.mikorosa.dziecoin;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CalculateHashTest {
+
+    @org.junit.jupiter.api.Test
+    void sha256sum() {
+        String resultingHash = CalculateHash.sha256sum("testing");
+        assertEquals("cf80cd8aed482d5d1527d7dc72fceff84e6326592848447d2dc0b0e87dfc9a90", resultingHash);
+    }
+
+    @org.junit.jupiter.api.Test
+    void md5sum() {
+        String resultingHash = CalculateHash.md5sum("testing");
+        assertEquals("ae2b1fca515949e5d54fb22b8ed95575", resultingHash);
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/pl/mikorosa/dziecoin/NFTTest.java b/src/test/java/pl/mikorosa/dziecoin/NFTTest.java
new file mode 100644
index 0000000..067ad75
--- /dev/null
+++ b/src/test/java/pl/mikorosa/dziecoin/NFTTest.java
@@ -0,0 +1,16 @@
+package pl.mikorosa.dziecoin;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class NFTTest {
+    @Test
+    void NFTContractGen() {
+        NFT nft = new NFT("stevejobs", "test");
+
+        String hash = CalculateHash.md5sum("stevejobstest");
+
+        assertEquals(hash, nft.getContract());
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/pl/mikorosa/dziecoin/database/DatabaseConnectionTest.java b/src/test/java/pl/mikorosa/dziecoin/database/DatabaseConnectionTest.java
new file mode 100644
index 0000000..93e229a
--- /dev/null
+++ b/src/test/java/pl/mikorosa/dziecoin/database/DatabaseConnectionTest.java
@@ -0,0 +1,42 @@
+package pl.mikorosa.dziecoin.database;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class DatabaseConnectionTest {
+
+    @Test
+    void select() {
+        DatabaseConnection db = new DatabaseConnection();
+        List<Map<String, Object>> rows = db.query("SELECT * FROM test");
+        int numRows = rows.size();
+
+        assertEquals(0, numRows);
+    }
+
+    @Test
+    void insertAndDelete() {
+        DatabaseConnection db = new DatabaseConnection();
+
+        List<Map<String, Object>> before = db.query("SELECT * FROM test");
+        int numRowsBefore = before.size();
+
+        db.update("INSERT INTO test VALUES (null, 'aaa')");
+
+        List<Map<String, Object>> rowsAfter = db.query("SELECT * FROM test");
+        int numRowsAfter = rowsAfter.size();
+
+        assertEquals(numRowsBefore + 1, numRowsAfter);
+
+        db.update("DELETE FROM test");
+
+        List<Map<String, Object>> rowsDeleted = db.query("SELECT * FROM test");
+        int numRowsDeleted = rowsDeleted.size();
+
+        assertEquals(numRowsAfter - 1, numRowsDeleted);
+    }
+}
\ No newline at end of file