Clean up TxValidatorTest & resource loading in other tests

Fix inspection warnings and other minor defects (unchecked casts, bad
'assert*' usage, unused assignments/declarations, missing null checks,
object equality on enum instances, needless statement lambdas, missing
final, redundant 'toString', needless visibility) in 'TxValidatorTest'.

Also, uniformise and slightly tidy resource loading in other test
classes, replacing 'Files.readAllBytes' with Java 11 'Files.readString'
(which assumes UTF-8 as desired, instead of the default charset).

core/src/test/java/bisq/core/app/BisqHelpFormatterTest.java

@@ -31,6 +31,8 @@
 import java.io.IOException;
 import java.io.PrintStream;
 
+import java.util.Objects;
+
 import org.junit.jupiter.api.Test;
 
 import static org.hamcrest.CoreMatchers.equalTo;
@@ -125,11 +127,11 @@ public void testHelpFormatter() throws IOException, URISyntaxException {
                 .defaultsTo(AnEnum.foo);
 
         ByteArrayOutputStream actual = new ByteArrayOutputStream();
-        String expected = new String(Files.readAllBytes(Paths.get(getClass().getResource("cli-output.txt").toURI())));
+        String expected = Files.readString(Paths.get(Objects.requireNonNull(getClass().getResource("cli-output.txt")).toURI()));
         if (System.getProperty("os.name").startsWith("Windows")) {
             // Load the expected content from a different file for Windows due to different path separator
             // And normalize line endings to LF in case the file has CRLF line endings
-            expected = new String(Files.readAllBytes(Paths.get(getClass().getResource("cli-output_windows.txt").toURI())))
+            expected = Files.readString(Paths.get(Objects.requireNonNull(getClass().getResource("cli-output_windows.txt")).toURI()))
                     .replaceAll("\\r\\n?", "\n");
         }
 

core/src/test/java/bisq/core/dao/node/full/rpc/BitcoindClientTest.java

@@ -36,6 +36,8 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 
+import java.util.Objects;
+
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -52,7 +54,6 @@
 import com.googlecode.jsonrpc4j.HttpException;
 import com.googlecode.jsonrpc4j.JsonRpcClientException;
 import com.googlecode.jsonrpc4j.RequestIDGenerator;
-import kotlin.text.Charsets;
 
 public class BitcoindClientTest {
     private static final String TEST_BLOCK_HASH = "015f37a20d517645a11a6cdd316049f41bc77b4a4057b2dd092114b78147f42c";
@@ -66,7 +67,7 @@ public class BitcoindClientTest {
     private boolean canConnect = true;
     private ByteArrayInputStream mockResponse;
     private ByteArrayInputStream mockErrorResponse;
-    private ByteArrayOutputStream mockOutputStream = new ByteArrayOutputStream();
+    private final ByteArrayOutputStream mockOutputStream = new ByteArrayOutputStream();
 
     @BeforeEach
     public void setUp() throws Exception {
@@ -116,7 +117,7 @@ public void testGetBlockCount_noConnection() {
     }
 
     @Test
-    public void testGetBlockCount_wrongCredentials() throws Exception {
+    public void testGetBlockCount_wrongCredentials() {
         mockResponseCode = 401;
 //        mockResponseCustomHeaders.put("WWW-Authenticate", "[Basic realm=\"jsonrpc\"]");
         assertThrows(HttpException.class, () -> client.getBlockCount());
@@ -218,8 +219,8 @@ private static ByteArrayInputStream toJsonIS(String json) {
 
     private static String readFromResourcesUnPrettified(String resourceName) {
         try {
-            var path = Paths.get(BitcoindClientTest.class.getResource(resourceName).toURI());
-            return new String(Files.readAllBytes(path), Charsets.UTF_8).replaceAll("(\\s+\\B|\\B\\s+|\\v)", "");
+            var path = Paths.get(Objects.requireNonNull(BitcoindClientTest.class.getResource(resourceName)).toURI());
+            return Files.readString(path).replaceAll("(\\s+\\B|\\B\\s+|\\v)", "");
         } catch (Exception e) {
             return "";
         }