Core: Decide "No tests" based on test count, not assert count

If a test has no assertions, that is generally by itself another
unrelated error. But more importantly, it is configurable, and
also something that we support on a per-test basis via
assert.expect(0) for which there are several use cases such
as when the tests only purpose is not to throw, either from
your source code, or from another helper library (e.g. Sinon
assertion's throwing).

Previously, if your test suite composed only of such tests,
or if you selective run such test only, it wrongly caused
the test runner to report a global error for "No tests."

Fixes #1405.
Closes #1449.

src/core.js

@@ -96,7 +96,7 @@ extend( QUnit, {
 
 		// Initialize the configuration options
 		extend( config, {
-			stats: { all: 0, bad: 0 },
+			stats: { all: 0, bad: 0, testCount: 0 },
 			started: 0,
 			updateRate: 1000,
 			autostart: true,

src/core/processing-queue.js

@@ -165,7 +165,7 @@ function done() {
 	const runtime = now() - config.started;
 	const passed = config.stats.all - config.stats.bad;
 
-	if ( config.stats.all === 0 ) {
+	if ( config.stats.testCount === 0 ) {
 
 		if ( config.filter && config.filter.length ) {
 			throw new Error( `No tests matched the filter "${config.filter}".` );

src/test.js

@@ -299,6 +299,7 @@ Test.prototype = {
 		this.runtime = now() - this.started;
 
 		config.stats.all += this.assertions.length;
+		config.stats.testCount += 1;
 		module.stats.all += this.assertions.length;
 
 		for ( i = 0; i < this.assertions.length; i++ ) {

test/cli/fixtures/expected/tap-outputs.js

@@ -186,6 +186,15 @@ ok 2 timeout > second
 # fail 1
 `,
 
+	"qunit zero-assertions.js":
+`TAP version 13
+ok 1 Zero assertions > has a test
+1..1
+# pass 1
+# skip 0
+# todo 0
+# fail 0`,
+
 	// in node 8, the stack trace includes 'at <anonymous>. But not in node 6 or 10.
 	"qunit qunit --filter 'no matches' test":
 `TAP version 13

test/cli/fixtures/zero-assertions.js

@@ -0,0 +1,8 @@
+QUnit.module( "Zero assertions", function() {
+	QUnit.test( "has a test", function( assert ) {
+		assert.expect( 0 );
+
+		// A test may expect zero assertions if its main purpose
+		// is to ensure there are no no run-time exceptions.
+	} );
+} );

test/cli/main.js

@@ -149,6 +149,15 @@ QUnit.module( "CLI Main", function() {
 		}
 	} ) );
 
+	QUnit.test( "allows running zero-assertion tests", co.wrap( function* ( assert ) {
+		const command = "qunit zero-assertions.js";
+		const execution = yield execute( command );
+
+		assert.equal( execution.code, 0 );
+		assert.equal( execution.stderr, "" );
+		assert.equal( execution.stdout, expectedOutput[ command ] );
+	} ) );
+
 	if ( semver.gte( process.versions.node, "9.0.0" ) ) {
 		QUnit.test( "callbacks and hooks from modules are properly released for garbage collection", co.wrap( function* ( assert ) {
 			const command = "node --expose-gc --allow-natives-syntax ../../../bin/qunit.js memory-leak/*.js";