Add 3 testing knowledge files from book review

- test-one-when-per-test: one WHEN per test, split if multiple actions
- ui-test-codeunit-naming: _UT suffix for TestPage-based codeunits
- test-feature-scenario-tags: [FEATURE]/[SCENARIO] comment structure

Based on patterns from Automatiserede tests med Business Central (Dieringer).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

custom/knowledge/testing/ui-test-codeunit-naming.md

@@ -0,0 +1,102 @@
+---
+bc-version: [all]
+domain: testing
+keywords: [test, ui, testpage, naming, suffix, codeunit, page-testing]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+## Description
+
+Test codeunits that interact with pages via `TestPage` must carry a `_UT` suffix
+(Unit Test — UI layer) in their name. This distinguishes them from codeunits that
+test business logic directly by calling codeunit/table procedures.
+
+The suffix signals to every reader that the codeunit opens pages, uses
+`TestPage.OpenNew()`, reads FactBox parts, or drives field validates through
+the page's `OnValidate` triggers — i.e. it exercises the UI layer, not just
+the logic layer.
+
+**Convention:**
+
+| Layer tested | Suffix | Example |
+|---|---|---|
+| Business logic (codeunits, tables) | *(none)* | `FindPriceTesting` |
+| Page / UI layer (`TestPage`) | `_UT` | `FindPriceTesting_UT` |
+
+A codeunit may contain **only** UI tests or **only** logic tests — never mix both
+in the same codeunit.
+
+## Anti Pattern
+
+```al
+// WRONG: UI test codeunit without _UT suffix
+codeunit 99007 "Find Price Page Testing"
+{
+    Subtype = Test;
+    // contains TestPage calls — should be named "Find Price Testing_UT"
+    ...
+}
+```
+
+```al
+// WRONG: mixing direct codeunit calls and TestPage calls in the same codeunit
+codeunit 99007 "Find Price Testing"
+{
+    Subtype = Test;
+
+    [Test]
+    procedure GetPrice_LogicTest()   // logic test — fine here
+    begin
+        FindPriceMgt.GetSalesPrice(...);
+    end;
+
+    [Test]
+    procedure Page_ShowsPrice_UT()   // UI test — belongs in separate _UT codeunit
+    var
+        FindPricePage: TestPage "Find Price";
+    begin
+        FindPricePage.OpenNew();
+        ...
+    end;
+}
+```
+
+## Best Practice
+
+```al
+// CORRECT: separate codeunits per layer
+
+// Logic tests — no _UT suffix
+codeunit 99006 "Find Price Testing"
+{
+    Subtype = Test;
+    [Test]
+    procedure GetPrice_CustomerPrice_ReturnsUnitPrice()
+    begin
+        FindPriceMgt.GetSalesPrice(...);
+    end;
+}
+
+// UI tests — _UT suffix
+codeunit 99007 "Find Price Testing_UT"
+{
+    Subtype = Test;
+    [Test]
+    procedure Page_EnterCustomerAndItem_FactBoxShowsPrice()
+    var
+        FindPricePage: TestPage "Find Price";
+    begin
+        FindPricePage.OpenNew();
+        FindPricePage.CustomerNo.SetValue(Customer."No.");
+        FindPricePage.ItemNo.SetValue(Item."No.");
+        Assert.AreEqual('100,00', FindPricePage.FindPriceInfo.UnitPrice.Value(), '');
+    end;
+}
+```
+
+## Object ID allocation
+
+Allocate adjacent IDs for the two related codeunits (e.g. 99006 logic, 99007 UI)
+so they sort together in the object list and their relationship is self-evident.