fix(shards): zero-sized shard should not include all tests (#19148)

Fixes #19073.

packages/playwright-test/src/runner.ts

@@ -431,8 +431,16 @@ export class Runner {
     projectSetupGroups.length = 0;
     projectSetupGroups.push(...shardSetupGroups);
 
+    if (!shardTests.size) {
+      // Filtering with "only semantics" does not work when we have zero tests - it leaves all the tests.
+      // We need an empty suite in this case.
+      rootSuite._entries = [];
+      rootSuite.suites = [];
+      rootSuite.tests = [];
+    } else {
       filterSuiteWithOnlySemantics(rootSuite, () => false, test => shardTests.has(test));
     }
+  }
 
   private async _run(options: RunOptions): Promise<FullResult> {
     const config = this._loader.fullConfig();

tests/playwright-test/shard.spec.ts

@@ -63,6 +63,15 @@ test('should respect shard=2/2', async ({ runInlineTest }) => {
   expect(result.output).toContain('test5-done');
 });
 
+test('should not produce skipped tests for zero-sized shards', async ({ runInlineTest }) => {
+  const result = await runInlineTest(tests, { shard: '10/10' });
+  expect(result.exitCode).toBe(0);
+  expect(result.passed).toBe(0);
+  expect(result.failed).toBe(0);
+  expect(result.skipped).toBe(0);
+  expect(result.output).not.toContain('-done');
+});
+
 test('should respect shard=1/2 in config', async ({ runInlineTest }) => {
   const result = await runInlineTest({
     ...tests,