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/asserterror-needs-expectederror-and-code.good.al

@@ -0,0 +1,26 @@
+codeunit 50408 "Test AssertError Good"
+{
+    Subtype = Test;
+
+    [Test]
+    procedure BlankNameIsRejectedWithSpecificError()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.Init();
+        Customer.Name := '';
+
+        // [WHEN] a mandatory field is blank
+        asserterror Customer.TestField(Name);
+
+        // [THEN] verify the SPECIFIC failure through a reusable Library helper
+        // instead of hardcoding the localized message and the 'TestField' code.
+        // ExpectedTestFieldError centralizes that knowledge, so the test keeps
+        // working when the caption or code changes; FieldCaption avoids pinning
+        // the field name as a literal.
+        Assert.ExpectedTestFieldError(Customer.FieldCaption(Name), '');
+    end;
+
+    var
+        Assert: Codeunit "Library Assert";
+}