Improve #subpath exception messages

Fixes #158

src/main/java/com/github/marschall/memoryfilesystem/NonEmptyPath.java

@@ -112,13 +112,13 @@ void checkNameRange(int beginIndex, int endIndex) {
       throw new IllegalArgumentException("beginIndex must not be negative but was " + beginIndex);
     }
     if (beginIndex >= nameCount) {
-      throw new IllegalArgumentException("beginIndex must not be bigger than " + nameCount + " but was " + beginIndex);
+      throw new IllegalArgumentException("beginIndex must be smaller than " + nameCount + " but was " + beginIndex);
     }
-    if (endIndex <= beginIndex) {
-      throw new IllegalArgumentException("endIndex must not be smaller than or equal to " + beginIndex + " but was " + beginIndex);
+    if (beginIndex >= endIndex) {
+      throw new IllegalArgumentException("beginIndex must be smaller than " + beginIndex + " but was " + beginIndex);
     }
     if (endIndex > nameCount) {
-      throw new IllegalArgumentException("endIndex must not be bigger than " + nameCount + " but was " + beginIndex);
+      throw new IllegalArgumentException("endIndex must be smaller than or equal to " + nameCount + " but was " + endIndex);
     }
   }
 
@@ -212,14 +212,14 @@ public Path normalize() {
           }
         } else {
           if (nameElementsSize == 1) {
-          // path is just "/.."
-          normalized = this.handleSingleDotDot(normalized);
-          modified = normalized != nameElements;
-          break;
-        } else {
-          normalized = this.handleDotDotNormalizationNotYetModified(nameElements, nameElementsSize, i);
-          modified = normalized != nameElements;
-        }
+            // path is just "/.."
+            normalized = this.handleSingleDotDot(normalized);
+            modified = normalized != nameElements;
+            break;
+          } else {
+            normalized = this.handleDotDotNormalizationNotYetModified(nameElements, nameElementsSize, i);
+            modified = normalized != nameElements;
+          }
         }
         continue;
       }

src/test/java/com/github/marschall/memoryfilesystem/FileSystemCompatibilityTest.java

@@ -358,4 +358,11 @@ void relativeSymlinks(boolean useDefault) throws IOException {
     }
   }
 
+  @CompatibilityTest
+  void subPath(boolean useDefault) {
+    FileSystem fileSystem = this.getFileSystem(useDefault);
+    Path target = fileSystem.getPath("target");
+    assertThrows(IllegalArgumentException.class, () -> target.subpath(0, 0));
+  }
+
 }

src/test/java/com/github/marschall/memoryfilesystem/PathTests.java

@@ -0,0 +1,41 @@
+package com.github.marschall.memoryfilesystem;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.IOException;
+import java.nio.file.FileSystem;
+import java.nio.file.Path;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+class PathTests {
+
+  @RegisterExtension
+  final FileSystemExtension extension = new FileSystemExtension();
+
+  @Test
+  void subPath() throws IOException {
+    try (FileSystem fileSystem = this.extension.getFileSystem()) {
+      Path absolutePath = fileSystem.getPath("/parent/child.txt");
+      assertEquals(fileSystem.getPath("parent/child.txt"), absolutePath.subpath(0, 2));
+      assertEquals(fileSystem.getPath("parent"), absolutePath.subpath(0, 1));
+      assertEquals(fileSystem.getPath("child.txt"), absolutePath.subpath(1, 2));
+
+      IllegalArgumentException e = assertThrows(IllegalArgumentException.class, () -> absolutePath.subpath(1, 1));
+      assertEquals("beginIndex must be smaller than 1 but was 1", e.getMessage());
+
+      e = assertThrows(IllegalArgumentException.class, () -> absolutePath.subpath(-1, 1));
+      assertEquals("beginIndex must not be negative but was -1", e.getMessage());
+
+      e = assertThrows(IllegalArgumentException.class, () -> absolutePath.subpath(0, 3));
+      assertEquals("endIndex must be smaller than or equal to 2 but was 3", e.getMessage());
+
+      e = assertThrows(IllegalArgumentException.class, () -> absolutePath.subpath(2, 1));
+      assertEquals("beginIndex must be smaller than 2 but was 2", e.getMessage());
+    }
+
+  }
+
+}