BAEL-4165 - Custom DLL Load - Fixing the "java.lang.UnsatisfiedLinkError" Error (#14393)

* first draft

* review 1

* review 1 - test setup

java-native/src/test/java/com/baeldung/unsatisfiedlink/JniUnsatisfiedLinkManualTest.java

@@ -0,0 +1,105 @@
+package com.baeldung.unsatisfiedlink;
+
+import static com.baeldung.unsatisfiedlink.JniUnsatisfiedLink.LIB_NAME;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.File;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class JniUnsatisfiedLinkManualTest {
+
+    static String osLibPrefix = "";
+    static String osLibSuffix = "";
+
+    @BeforeAll
+    static void setup() {
+        String osName = System.getProperty("os.name")
+            .toLowerCase();
+
+        if (osName.contains("win")) {
+            osLibSuffix = ".dll";
+        } else if (osName.contains("nix") || osName.contains("nux") || osName.contains("mac")) {
+            osLibPrefix = "lib";
+            osLibSuffix = ".so";
+            if (osName.contains("mac")) {
+                osLibPrefix = "lib";
+                osLibSuffix = ".dylib";
+            }
+        } else {
+            throw new UnsupportedOperationException("Unsupported operating system: " + osName);
+        }
+    }
+
+    @Test
+    public void whenCorrectLibName_thenLibLoaded() {
+        assertDoesNotThrow(() -> {
+            System.loadLibrary(LIB_NAME);
+            new JniUnsatisfiedLink().test();
+        });
+    }
+
+    @Test
+    public void whenIncorrectLibName_thenLibNotFound() {
+        String libName = osLibPrefix + LIB_NAME + osLibSuffix;
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(libName));
+
+        assertEquals(String.format("no %s in java.library.path", libName), error.getMessage());
+    }
+
+    @Test
+    public void whenLoadLibraryContainsPathSeparator_thenErrorThrown() {
+        String libName = "/" + LIB_NAME;
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(libName));
+
+        assertEquals(String.format("Directory separator should not appear in library name: %s", libName), error.getMessage());
+    }
+
+    @Test
+    public void whenLoadWithoutAbsolutePath_thenErrorThrown() {
+        String libName = LIB_NAME;
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.load(libName));
+
+        assertEquals(String.format("Expecting an absolute path of the library: %s", libName), error.getMessage());
+    }
+
+    @Test
+    public void whenUnlinkedMethod_thenErrorThrown() {
+        System.loadLibrary(LIB_NAME);
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> new JniUnsatisfiedLink().nonexistentDllMethod());
+
+        assertTrue(error.getMessage()
+            .contains("JniUnsatisfiedLink.nonexistentDllMethod"));
+    }
+
+    @Test
+    public void whenIncompatibleArchitecture_thenErrorThrown() {
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(LIB_NAME + "32"));
+
+        assertTrue(error.getMessage()
+            .contains("wrong ELF class: ELFCLASS32"));
+    }
+
+    @Test
+    public void whenCorruptedFile_thenErrorThrown() {
+        String libPath = System.getProperty("java.library.path");
+        assertNotNull(libPath);
+
+        String dummyLib = LIB_NAME + "-dummy";
+        assertTrue(new File(libPath, osLibPrefix + dummyLib + osLibSuffix).isFile());
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(dummyLib));
+
+        assertTrue(error.getMessage()
+            .contains("file too short"));
+    }
+}