Test behaviour of fs.getName/getDir with relative paths

It's not entirely clear what the correct behaviour of fs.getDir("..")
should be, and there's not much consensus between various languages.

I think the intended behaviour of this function is to move "up" one
directory level in the path, meaning it should return "../..".

projects/core/src/main/java/dan200/computercraft/core/filesystem/FileSystem.java

@@ -122,6 +122,10 @@ public class FileSystem {
         }
 
         var lastSlash = path.lastIndexOf('/');
+
+        // If the trailing segment is a "..", then just append another one.
+        if (path.substring(lastSlash < 0 ? 0 : lastSlash + 1).equals("..")) return path + "/..";
+
         if (lastSlash >= 0) {
             return path.substring(0, lastSlash);
         } else {

projects/core/src/test/resources/test-rom/spec/apis/fs_spec.lua

@@ -160,6 +160,41 @@ describe("The fs library", function()
         end)
     end)
 
+    describe("fs.getName", function()
+        it("returns 'root' for the empty path", function()
+            expect(fs.getName("")):eq("root")
+            expect(fs.getName("foo/..")):eq("root")
+        end)
+
+        it("returns the file name", function()
+            expect(fs.getName("foo/bar")):eq("bar")
+            expect(fs.getName("foo/bar/")):eq("bar")
+            expect(fs.getName("../foo")):eq("foo")
+        end)
+
+        it("returns '..' for parent directories", function()
+            expect(fs.getName("..")):eq("..")
+        end)
+    end)
+
+    describe("fs.getDir", function()
+        it("returns '..' for the empty path", function()
+            expect(fs.getDir("")):eq("..")
+            expect(fs.getDir("foo/..")):eq("..")
+        end)
+
+        it("returns the directory name", function()
+            expect(fs.getDir("foo/bar")):eq("foo")
+            expect(fs.getDir("foo/bar/")):eq("foo")
+            expect(fs.getDir("../foo")):eq("..")
+        end)
+
+        it("returns '..' for parent directories", function()
+            expect(fs.getDir("..")):eq("../..")
+            expect(fs.getDir("../..")):eq("../../..")
+        end)
+    end)
+
     describe("fs.getSize", function()
         it("fails on non-existent nodes", function()
             expect.error(fs.getSize, "rom/x"):eq("/rom/x: No such file")