test(genesis): adds file loader tests

rskj-core/src/main/java/org/ethereum/core/genesis/GenesisLoaderImpl.java

@@ -41,13 +41,10 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.FileInputStream;
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.math.BigInteger;
 import java.nio.file.Files;
-import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.HashMap;
 import java.util.Map;
@@ -237,21 +234,16 @@ private void setupPrecompiledContractsStorage(Repository repository) {
 
     public static InputStream loadGenesisFile(String fileName) {
         InputStream inputStream = GenesisLoaderImpl.class.getResourceAsStream("/genesis/" + fileName);
-
         if (inputStream != null) {
             return inputStream;
         }
 
-        Path filePath = Paths.get(fileName);
-        if (Files.exists(filePath)) {
-            try {
-                return new FileInputStream(filePath.toFile());
-            } catch (FileNotFoundException e) {
-                logger.error(e.getLocalizedMessage());
-            }
+        try {
+            return Files.newInputStream(Paths.get(fileName));
+        } catch (Exception e) {
+            logger.error("Could not load file due to:", e);
+            return null;
         }
-
-        return null;
     }
 
     public static void loadGenesisInitalState(Repository repository, Genesis genesis) {

rskj-core/src/test/java/org/ethereum/core/genesis/GenesisLoaderImplTest.java

@@ -0,0 +1,74 @@
+package org.ethereum.core.genesis;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Path;
+import java.util.Objects;
+
+class GenesisLoaderImplTest {
+    private final String GENESIS_FILE_NAME = "temp_genesis.json";
+
+    private final String RESOURCES_GENESIS_FILE_PATH = Objects.requireNonNull(GenesisLoaderImpl.class.getResource("/genesis")).getPath() + "/" + GENESIS_FILE_NAME;
+
+    @SuppressWarnings("ResultOfMethodCallIgnored")
+    private boolean isStreamReadable(InputStream stream) {
+        try {
+            stream.read();
+            return true;
+        } catch (IOException e) {
+            return false;
+        }
+    }
+
+    @BeforeEach
+    public void createTempFiles() throws IOException {
+        boolean created = (new File(RESOURCES_GENESIS_FILE_PATH)).createNewFile();
+        Assertions.assertTrue(created);
+    }
+
+    @AfterEach
+    public void cleanUpFiles() {
+        boolean deleted = (new File(RESOURCES_GENESIS_FILE_PATH)).delete();
+        Assertions.assertTrue(deleted);
+    }
+
+    @Test
+    void loadGenesisFile_fromResourcesDir() {
+        InputStream genesisFileStream = GenesisLoaderImpl.loadGenesisFile(GENESIS_FILE_NAME);
+        assert genesisFileStream != null;
+
+        Assertions.assertTrue(isStreamReadable(genesisFileStream));
+    }
+
+    @Test
+    void loadGenesisFile_missingFile_inResourcesDir() {
+        File genesisFile = new File("non-existent-file.json");
+
+        Assertions.assertNull(GenesisLoaderImpl.loadGenesisFile(genesisFile.getPath()));
+    }
+
+    @Test
+    void loadGenesisFile_fromSystem(@TempDir Path tempGenesisDir) throws IOException {
+        File genesisFile = new File(tempGenesisDir + "/" + GENESIS_FILE_NAME);
+        Assertions.assertTrue(genesisFile.createNewFile());
+        InputStream genesisFileStream = GenesisLoaderImpl.loadGenesisFile(genesisFile.getPath());
+        assert genesisFileStream != null;
+
+        Assertions.assertTrue(isStreamReadable(genesisFileStream));
+    }
+
+    @Test
+    void loadGenesisFile_missingFile_inSystem(@TempDir Path tempGenesisDir) {
+        File genesisFile = new File(tempGenesisDir + "/non-existent-file.json");
+
+        Assertions.assertNull(GenesisLoaderImpl.loadGenesisFile(genesisFile.getPath()));
+    }
+
+}