Add testing knowledge: UI handlers, table relations, asserterror, fixtures (P1+P2) (#62)

* Add testing knowledge: UI handlers, table relations, asserterror, fixtures (P1+P2)

Six BC-specific testing-domain knowledge articles in community/knowledge/testing/, each with .good.al/.bad.al samples:

- ui-calls-require-test-handlers
- tablerelation-requires-prerequisite-records
- handlers-enqueue-never-assert
- handlerfunctions-attribute-must-match-ui-path
- asserterror-needs-expectederror-and-code
- use-library-codeunits-for-test-fixtures

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Move testing knowledge from community to microsoft layer

Relocates the six P1+P2 testing-domain articles (18 files: .md + .good.al + .bad.al each) from community/knowledge/testing/ to microsoft/knowledge/testing/ per maintainer request. Pure git-mv rename; no content or frontmatter changes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review: merge handler articles, adopt enqueue-driven pattern

Respond to @nikolakukrika's review on #62:

- Merge ui-calls-require-test-handlers, handlerfunctions-attribute-must-match-ui-path
  and handlers-enqueue-never-assert into a single ui-handlers-in-tests article.
- Adopt the enqueue-from-test / dequeue-and-assert-in-handler pattern using
  Assert.ExpectedConfirm/ExpectedMessage (substring match), with Initialize()
  clearing LibraryVariableStorage and AssertEmpty() proving exact call counts.
- asserterror sample now uses Assert.ExpectedTestFieldError + FieldCaption instead
  of hardcoded message/code; article text points to the library helpers.
- Drop the tablerelation article and fold its test-relevant ordering point
  (relations checked on Validate/Insert(true); build parents first) into
  use-library-codeunits-for-test-fixtures.

Article count 198 -> 195.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

microsoft/knowledge/testing/ui-handlers-in-tests.good.al

@@ -0,0 +1,57 @@
+codeunit 50400 "Test UI Handlers Good"
+{
+    Subtype = Test;
+
+    [Test]
+    [HandlerFunctions('ConfirmHandler,PostMessageHandler')]
+    procedure PostDocumentConfirmsAndMessages()
+    begin
+        Initialize();
+
+        // [GIVEN] the test enqueues, in interaction order, what each handler
+        //         will see and how it should answer: the Confirm's expected
+        //         question plus the reply to return, then the expected Message.
+        LibraryVariableStorage.Enqueue('Post this document?'); // expected question (substring)
+        LibraryVariableStorage.Enqueue(true);                  // reply ConfirmHandler returns
+        LibraryVariableStorage.Enqueue('Posting completed.');  // expected message (substring)
+
+        // [WHEN] the code under test raises the Confirm and then the Message
+        RunPostingThatConfirmsAndMessages();
+
+        // [THEN] every enqueued expectation was consumed exactly once
+        LibraryVariableStorage.AssertEmpty();
+    end;
+
+    local procedure Initialize()
+    begin
+        // Clear leftover values so a value leaked by an earlier test cannot
+        // cascade into this one.
+        LibraryVariableStorage.Clear();
+    end;
+
+    local procedure RunPostingThatConfirmsAndMessages()
+    begin
+        // Stands in for the production routine that confirms, then messages.
+        if Confirm('Post this document?', false) then
+            Message('Posting completed.');
+    end;
+
+    [ConfirmHandler]
+    procedure ConfirmHandler(Question: Text[1024]; var Reply: Boolean)
+    begin
+        // Verify the RIGHT dialog fired (substring match), then return the
+        // reply the test enqueued for it.
+        Assert.ExpectedConfirm(LibraryVariableStorage.DequeueText(), Question);
+        Reply := LibraryVariableStorage.DequeueBoolean();
+    end;
+
+    [MessageHandler]
+    procedure PostMessageHandler(Message: Text[1024])
+    begin
+        Assert.ExpectedMessage(LibraryVariableStorage.DequeueText(), Message);
+    end;
+
+    var
+        Assert: Codeunit "Library Assert";
+        LibraryVariableStorage: Codeunit "Library - Variable Storage";
+}