fix(build): count passed and failed, not merely discovered, tests

Follow-up to the previous gate, which used TotalCount minus NotRunCount.
That misses a suite where every test is skipped: skipped tests are neither
NotRun nor executed-with-a-result, so the subtraction stays positive and
the build passes having run nothing.

Measured against Pester 6.1.0:

  empty test directory     Total 0    Passed 0  Failed 0  Skipped 0  NotRun 0
  filter matching no test  Total 120  Passed 0  Failed 0  Skipped 0  NotRun 120
  every test -Skip         Total 3    Passed 0  Failed 0  Skipped 3  NotRun 0

Filtering on the per-test .Executed property does not distinguish the
third case either -- skipped tests report Executed = $true. Only
PassedCount plus FailedCount separates a suite that ran from one that
did not, so the gate uses that.

Verified all three: all-skipped exits 1, empty directory exits 1, and a
normal run with two legitimate skips reports 118 passed and exits 0.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G1CarQG8VibNFxw4cN53Zs

Author: tablackburn

build.psake.ps1

@@ -256,12 +256,21 @@ Task -Name 'UnitTest' -Depends 'Build' -PreCondition $unitTestPreReqs -Descripti
         #
         # Test.Enabled is the deliberate opt-out and is handled in the PreCondition;
         # reaching here having run nothing is a fault either way.
-        # Cast before subtracting: when nothing is discovered at all these counts come
-        # back null, and null arithmetic would otherwise leave the message blank.
-        $discoveredCount = [int]$testResult.TotalCount
-        $notRunCount = [int]$testResult.NotRunCount
-        if (($discoveredCount - $notRunCount) -le 0) {
-            throw "Pester executed no tests under [$($PSBPreference.Test.RootDir)] (discovered $discoveredCount, not run $notRunCount). Refusing to report success without running tests."
+        # Count tests that actually produced a result. Measured against Pester 6.1.0,
+        # three ways to reach "nothing ran" that every failure count reads as success:
+        #
+        #   empty test directory     -> Total 0,   Passed 0, Failed 0, Skipped 0, NotRun 0
+        #   filter matching no test  -> Total 120, Passed 0, Failed 0, Skipped 0, NotRun 120
+        #   every test -Skip         -> Total 3,   Passed 0, Failed 0, Skipped 3, NotRun 0
+        #
+        # TotalCount minus NotRunCount misses the third, and so does filtering on the
+        # per-test .Executed property -- skipped tests report Executed = $true. Only
+        # passed-plus-failed distinguishes a suite that ran from one that did not.
+        # Casts are deliberate: with nothing discovered these come back null.
+        $ranCount = [int]$testResult.PassedCount + [int]$testResult.FailedCount
+        if ($ranCount -le 0) {
+            $counts = "discovered $([int]$testResult.TotalCount), skipped $([int]$testResult.SkippedCount), not run $([int]$testResult.NotRunCount)"
+            throw "Pester ran no tests under [$($PSBPreference.Test.RootDir)] ($counts). Refusing to report success without running tests."
         }
     }
     finally {