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name: tdd description: >- AL test development patterns with telemetry verification. MANDATORY when: (1) planning test implementation, (2) creating new tests, (3) modifying existing tests. Invoke proactively at ALL three stages. PLANNING: Structure plans with Red-Green-Refactor phases and use TodoWrite to track progress through each phase. CRITICAL RULE: DEBUG-* telemetry must be ZERO at both task START and END.

AL Test Development Patterns

Planning Test Work

When planning any test-related task, structure your plan with Red-Green-Refactor phases:

Plan Structure

Phase 1 - Red (Design):

• Identify test scenarios to cover
• Plan DEBUG-* telemetry checkpoints for verification
• Determine which code paths need proof of execution

Phase 2 - Green (Implementation):

• Write test code with DEBUG-TEST-START markers
• Add DEBUG-* checkpoints in production code at decision points
• Run tests and verify telemetry.jsonl shows correct paths

Phase 3 - Refactor (Cleanup):

• Remove ALL DEBUG-* telemetry from test and production code
• Verify zero DEBUG-* calls remain

TodoWrite Integration

When implementing tests, create todos for each phase:

Copy1. [Red] Add DEBUG-TEST-START to <TestName>
2. [Red] Add DEBUG-BRANCH-* checkpoints to <ProductionCode>
3. [Green] Run al-build and verify test passes
4. [Green] Verify correct path in telemetry.jsonl
5. [Refactor] Remove DEBUG-* from production code
6. [Refactor] Remove DEBUG-TEST-START from test code
7. [Refactor] Verify zero DEBUG-* calls remain

This structure ensures every test task follows the complete verification cycle.

DEBUG Telemetry is Always Temporary

Expected starting state: Zero DEBUG-* telemetry calls in both production code (app/src/) and test code (test/src/).

Why: DEBUG telemetry is temporary scaffolding for proving code paths during development. It is NOT production instrumentation. If you find existing DEBUG-* calls, they indicate incomplete previous work.

Lifecycle:

1. Start clean (expect no DEBUG-* anywhere)
2. Add DEBUG-* calls during Red phase to prove execution
3. Verify in telemetry.jsonl during Green phase
4. Remove ALL DEBUG- calls during Refactor phase* (REQUIRED)
5. End clean (no DEBUG-* anywhere)

If you find existing DEBUG- calls:*

• Complete the previous work (remove them after verification), OR
• Remove them immediately if they're orphaned from abandoned work

Assertions vs DEBUG Telemetry

They verify different things:

The False Positive Problem:

Assertions can pass even when test setup is wrong. Example:

• Test intends to verify "Sales Line branch" produces Quantity=7
• Assertion passes: Assert.AreEqual(7, ActualQuantity)
• But test setup was wrong—code actually took the "Config Header branch"
• That branch also happened to produce Quantity=7 (coincidence)
• Without production telemetry, you cannot detect this

Solution: Production code telemetry proves which path ran:

• DEBUG-TEST-START in test → identifies which test is running
• DEBUG-* in production → proves which branch executed
• Correlation → confirms "Test X exercised code path Y"

Quick Start

Every test procedure you write MUST include:

CopyFeatureTelemetry.LogUsage('DEBUG-TEST-START', 'Testing', '<ExactProcedureName>');

as the FIRST line after variable declarations. This is non-negotiable.

Core rule

Telemetry verification is manual—do not add telemetry parsing/assertions to AL tests.

Mandatory: Test-Start Telemetry Checkpoint

Every test procedure MUST begin with a telemetry checkpoint immediately after variable declarations:

Copy[Test]
procedure GivenX_WhenY_ThenZ()
var
    FeatureTelemetry: Codeunit "Feature Telemetry";
    // other variables...
begin
    // FIRST LINE - Always add this checkpoint
    FeatureTelemetry.LogUsage('DEBUG-TEST-START', 'Testing', 'GivenX_WhenY_ThenZ');

    // [SCENARIO] ...
    // [GIVEN] ...
    // [WHEN] ...
    // [THEN] ...
end;

Why Test-Start Telemetry is Critical

Production code telemetry (e.g., pricing calculations, rule evaluations) can emit from multiple tests. Without test-start markers:

• Cannot determine which test triggered a specific log entry
• Cannot correlate DEBUG-* checkpoints in production code to the test that exercised them
• Cannot isolate test failures when multiple tests touch the same code paths

With test-start markers in telemetry.jsonl:

Copy{"eventId":"DEBUG-TEST-START","message":"GivenX_WhenY_ThenZ",...}
{"eventId":"DEBUG-PRICING-CALC","message":"Configuration method selected",...}
{"eventId":"DEBUG-COMPONENT-TOTAL","message":"Sum: 150.00",...}

Now you can grep for your test name and see all subsequent logs belong to that test.

Workflow

1) Red: add temporary telemetry checkpoints

Step A (REQUIRED): Add test-start checkpoint as FIRST line after declarations:

CopyFeatureTelemetry.LogUsage('DEBUG-TEST-START', 'Testing', '<ExactProcedureName>');

Step B (REQUIRED): Add branch checkpoints in PRODUCTION code at decision points:

Copy// In the function under test (production code)
if SalesLine.FindFirst() then begin
    FeatureTelemetry.LogUsage('DEBUG-BRANCH-SALESLINE', 'FeatureName', 'Sales Line found');
    // ... Sales Line path
end else begin
    FeatureTelemetry.LogUsage('DEBUG-BRANCH-NOSALESLINE', 'FeatureName', 'Using Config Header');
    // ... Config Header path
end;

Rules:

• Use FeatureTelemetry.LogUsage() (not Session.LogMessage())
• Use exact procedure name in test-start for grep-ability
• Keep event IDs stable and searchable (DEBUG-TEST-START, DEBUG-BRANCH-*)
• Use Format() for non-text values in custom dimensions
• Production code markers are REQUIRED—they verify test setup correctness

2) Green: make it pass and prove the path

1. Run the full test gate (see skill al-build)
2. Confirm test pass/fail in .output/TestResults/last.xml
3. Manually confirm expected branch ran in .output/TestResults/telemetry.jsonl

Useful telemetry fields: eventId, message, testCodeunit, testProcedure, callStack, customDimensions

3) Refactor: remove temporary logs

Once tests are verified and green, delete all DEBUG-* telemetry from both locations:

Production code:

• Remove branch checkpoints (e.g., DEBUG-PRICING-CALC, DEBUG-COMPONENT-TOTAL)
• Keep only long-lived production instrumentation (non-DEBUG event IDs)

Test code:

• Remove test-start checkpoints (DEBUG-TEST-START)
• Remove any other DEBUG-* calls added for verification

Both must be cleaned up—leaving DEBUG telemetry in either location pollutes logs and signals incomplete work.

Analyzing Telemetry Correlation

After running tests, correlate logs to specific tests:

Copy# Find all logs from a specific test
Select-String -Path .output/TestResults/telemetry.jsonl -Pattern "GivenX_WhenY_ThenZ"

# Find test-start markers to see test execution order
Select-String -Path .output/TestResults/telemetry.jsonl -Pattern "DEBUG-TEST-START"

In telemetry.jsonl, logs appear in execution order. After a DEBUG-TEST-START entry, all subsequent logs belong to that test until the next DEBUG-TEST-START.

Telemetry Correlation Example

After running tests, telemetry.jsonl shows execution order:

CopyTest 1: GivenSalesLineExists...
  DEBUG-TEST-START → GivenSalesLineExists...
  DEBUG-BRANCH-SALESLINE → Sales Line found     ✓ Correct path

Test 2: GivenNoSalesLine...
  DEBUG-TEST-START → GivenNoSalesLine...
  DEBUG-BRANCH-NOSALESLINE → Using Config Header  ✓ Correct path

If wrong telemetry appears, test setup is broken:

CopyTest 1: GivenSalesLineExists...  (expects SALESLINE branch)
  DEBUG-TEST-START → GivenSalesLineExists...
  DEBUG-BRANCH-NOSALESLINE → Using Config Header  ✗ WRONG PATH!

This catches bugs that assertions cannot—the assertion might still pass if both paths produce the same value.

BC Event Subscriber Telemetry Pattern

When tests fail because standard BC code isn't behaving as expected, we can't add DEBUG telemetry directly to BC code. Instead, we create temporary event subscribers that emit telemetry from BC's published events.

This pattern applies to any BC subsystem—pricing, posting, warehouse, manufacturing, etc. The pricing engine example below is just one application of a universal debugging technique.

When to Use

• BC subsystem returns unexpected values (pricing engine, posting routines, document handling, etc.)
• Need to understand which BC code paths are executing
• Standard BC behavior is opaque and assertions alone can't diagnose the issue
• Any situation where you need visibility into what standard BC is doing internally

Finding Relevant BC Events

Use the bc-w1-reference skill to find events in the BC subsystem you're debugging:

Copy# Find integration events in a specific subsystem
rg -n "IntegrationEvent" "../_aldoc/bc-w1/BaseApp/Source/Base Application/Pricing/"
rg -n "IntegrationEvent" "../_aldoc/bc-w1/BaseApp/Source/Base Application/Sales/"
rg -n "IntegrationEvent" "../_aldoc/bc-w1/BaseApp/Source/Base Application/Purchases/"

# Find events by name pattern
rg -l "OnAfterPost" "../_aldoc/bc-w1/BaseApp/Source/Base Application/"
rg -l "OnBeforeValidate" "../_aldoc/bc-w1/BaseApp/Source/Base Application/"

Or use the Task tool with subagent_type=Explore to search the bc-w1 mirror:

CopyTask tool:
  subagent_type: Explore
  prompt: "Search the BC W1 source mirror for integration events in [subsystem].
           Find events that fire during [specific operation] that could help debug [issue]."

Implementation Steps

1. Find relevant BC events using bc-w1-reference skill (see above)

2. Create temporary debug subscriber codeunit in test folder:

Copycodeunit 50XXX "NALICF Debug [Subsystem] Subsc"
{
    Access = Internal;

    [EventSubscriber(ObjectType::Codeunit, Codeunit::"[BC Codeunit]", '[EventName]', '', false, false)]
    local procedure OnAfter[Event](var [Params])
    var
        FeatureTelemetry: Codeunit "Feature Telemetry";
    begin
        FeatureTelemetry.LogUsage('DEBUG-BC-[SUBSYSTEM]-[EVENT]', '[Area]',
            StrSubstNo('[Description]: %1', [RelevantValue]));
    end;
}

1. Run tests and analyze telemetry.jsonl — Correlate BC events with test execution:

CopySelect-String -Path .output/TestResults/telemetry.jsonl -Pattern "DEBUG-BC-"

1. Delete the subscriber codeunit after debugging — It's temporary scaffolding, not production code.

Example: BC Pricing Engine

This example shows debugging the Price Calculation - V16 codeunit, but the same approach works for any BC subsystem (posting codeunits, document management, inventory, etc.):

Copycodeunit 50105 "NALICF Debug Price Subsc"
{
    Access = Internal;

    [EventSubscriber(ObjectType::Codeunit, Codeunit::"Price Calculation - V16", 'OnAfterFindLines', '', false, false)]
    local procedure OnAfterFindLines(var PriceListLine: Record "Price List Line"; AmountType: Enum "Price Amount Type"; var IsHandled: Boolean)
    var
        FeatureTelemetry: Codeunit "Feature Telemetry";
    begin
        FeatureTelemetry.LogUsage('DEBUG-BC-PRICING-FINDLINES', 'Pricing',
            StrSubstNo('Found %1 lines, IsHandled=%2', PriceListLine.Count(), IsHandled));
    end;

    [EventSubscriber(ObjectType::Codeunit, Codeunit::"Price Calculation - V16", 'OnAfterCalcBestAmount', '', false, false)]
    local procedure OnAfterCalcBestAmount(var PriceListLine: Record "Price List Line")
    var
        FeatureTelemetry: Codeunit "Feature Telemetry";
    begin
        FeatureTelemetry.LogUsage('DEBUG-BC-PRICING-BESTAMOUNT', 'Pricing',
            StrSubstNo('BestAmount: UnitPrice=%1, Status=%2', PriceListLine."Unit Price", PriceListLine.Status));
    end;
}

This revealed the V16 pricing engine wasn't enabled—leading to the fix:

CopyLibraryPriceCalculation.EnableExtendedPriceCalculation();
LibraryPriceCalculation.SetupDefaultHandler("Price Calculation Handler"::"Business Central (Version 16.0)");

Other Subsystem Examples

The same pattern applies to any BC area:

Use bc-w1-reference to discover the specific events available in each subsystem.

Key Points

• Subscriber codeunits are temporary—delete after debugging
• Use DEBUG-BC-* prefix to distinguish from app telemetry
• Place in test folder (not app folder) to avoid shipping debug code
• Combine with test-start telemetry to correlate BC events to specific tests
• Use bc-w1-reference skill to find relevant events before creating subscribers
• This pattern works for any BC subsystem, not just pricing

Test Structure Requirements

Transaction Model Best Practices

Default: Do NOT specify [TransactionModel] on test methods.

Microsoft's standard BC tests (40,000+ test methods) rely on the TestRunner's TestIsolation property rather than individual test attributes. Only ~3% of BC standard tests specify [TransactionModel].

How isolation works in BC:

When to use [TransactionModel] (exceptions only):

Why NOT to default to AutoRollback:

1. Breaks if production code calls Commit() (posting, background jobs)
2. Duplicates TestRunner isolation if already configured
3. Inconsistent with Microsoft's own test patterns
4. Limits ability to test realistic business scenarios

Template Reference

When creating new test codeunits, follow the structure in NALICFTestTemplate.Codeunit.al.

Key elements:

1. Subtype = Test, Access = Internal
2. FeatureTelemetry and IsInitialized variables
3. Gherkin comments: [SCENARIO], [GIVEN], [WHEN], [THEN]
4. Initialize() procedure with IsInitialized guard
5. Test-start telemetry as first line after declarations
6. No [TransactionModel] by default — let TestRunner handle isolation

New test codeunit setup:

1. Create file in appropriate folder: test/src/Workflows/<Feature>/NALICF<Feature>Test.Codeunit.al
2. Allocate ID using al-object-id-allocator skill
3. Only add [TransactionModel] if you have a specific reason (see table above)