acceptance: apply sharding only to the full TestAccept run

TestInprocessMode calls testAccept with a specific singleTest
("selftest/basic"). The shard filter lived in getTests(), so it ran
before singleTest selection and could strip the requested test out of
the shard, failing with "did not match any tests" on every shard that
didn't own selftest/basic.

Move the shard filter into a shardTests helper applied in testAccept
only when singleTest == "", leaving named-test selection unsharded.

Co-authored-by: Isaac

Author: denik

acceptance/acceptance_test.go

@@ -350,6 +350,10 @@ func testAccept(t *testing.T, inprocessMode bool, singleTest string) int {
 			return n != singleTest
 		})
 		require.NotEmpty(t, testDirs, "singleTest=%#v did not match any tests\n%#v", singleTest, testDirs)
+	} else {
+		// Sharding applies only to the full run. A specific singleTest (e.g.
+		// TestInprocessMode) must never be filtered out by the shard split.
+		testDirs = shardTests(testDirs)
 	}
 
 	skippedDirs := 0
@@ -510,21 +514,25 @@ func getTests(t *testing.T) []string {
 	require.NoError(t, err)
 
 	slices.Sort(testDirs)
+	return testDirs
+}
 
-	// Shard the test list when SHARD_TOTAL > 1. Tests are sorted above so the
-	// split is deterministic and stable across runs.
-	if total, _ := strconv.Atoi(os.Getenv("SHARD_TOTAL")); total > 1 {
-		index, _ := strconv.Atoi(os.Getenv("SHARD_INDEX"))
-		sharded := testDirs[:0]
-		for i, d := range testDirs {
-			if i%total == index {
-				sharded = append(sharded, d)
-			}
+// shardTests returns the subset of testDirs assigned to this CI shard when
+// SHARD_TOTAL > 1, or testDirs unchanged otherwise. testDirs must be sorted so
+// the split is deterministic and stable across runs.
+func shardTests(testDirs []string) []string {
+	total, _ := strconv.Atoi(os.Getenv("SHARD_TOTAL"))
+	if total <= 1 {
+		return testDirs
+	}
+	index, _ := strconv.Atoi(os.Getenv("SHARD_INDEX"))
+	sharded := testDirs[:0]
+	for i, d := range testDirs {
+		if i%total == index {
+			sharded = append(sharded, d)
 		}
-		testDirs = sharded
 	}
-
-	return testDirs
+	return sharded
 }
 
 func validateTestPhase(phase int) error {