From ed2c5639d47734db226be2b03d6b6379cb8525ba Mon Sep 17 00:00:00 2001
From: Lars den Bakker <larsdenbakker@gmail.com>
Date: Fri, 2 Oct 2020 22:19:09 +0200
Subject: [PATCH] feat(test-runner): improve error message when no browsers are
 configured

---
 .changeset/khaki-carpets-tan.md                  |  6 ++++++
 .../test-runner-core/src/runner/TestRunner.ts    | 16 ++++++++++++----
 packages/test-runner/web-test-runner.config.mjs  |  1 +
 3 files changed, 19 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/khaki-carpets-tan.md

diff --git a/.changeset/khaki-carpets-tan.md b/.changeset/khaki-carpets-tan.md
new file mode 100644
index 000000000..c42dabbc1
--- /dev/null
+++ b/.changeset/khaki-carpets-tan.md
@@ -0,0 +1,6 @@
+---
+'@web/test-runner': patch
+'@web/test-runner-core': patch
+---
+
+improve error message when no browsers are configured
diff --git a/packages/test-runner-core/src/runner/TestRunner.ts b/packages/test-runner-core/src/runner/TestRunner.ts
index 17770da02..aa7aa5dee 100644
--- a/packages/test-runner-core/src/runner/TestRunner.ts
+++ b/packages/test-runner-core/src/runner/TestRunner.ts
@@ -39,16 +39,24 @@ export class TestRunner extends EventEmitter<EventMap> {
 
   constructor(config: TestRunnerCoreConfig, groupConfigs: TestRunnerGroupConfig[] = []) {
     super();
+    if (!config.manual && (!config.browsers || config.browsers.length === 0)) {
+      throw new Error('No browsers are configured to run tests');
+    }
+
+    if (config.manual && config.watch) {
+      throw new Error('Cannot combine the manual and watch options.');
+    }
+
+    if (config.open && !config.manual) {
+      throw new Error('The open option requires the manual option to be set.');
+    }
+
     const { sessionGroups, testFiles, testSessions, browsers } = createTestSessions(
       config,
       groupConfigs,
     );
     this.config = config;
 
-    if (this.config.manual && this.config.watch) {
-      throw new Error('Cannot combine the manual and watch options.');
-    }
-
     this.testFiles = testFiles;
     this.browsers = browsers;
     this.browserNames = Array.from(new Set(this.browsers.map(b => b.name)));
diff --git a/packages/test-runner/web-test-runner.config.mjs b/packages/test-runner/web-test-runner.config.mjs
index 5c86f32a0..51cd6f605 100644
--- a/packages/test-runner/web-test-runner.config.mjs
+++ b/packages/test-runner/web-test-runner.config.mjs
@@ -2,4 +2,5 @@ export default {
   rootDir: '../../',
   preserveSymlinks: true,
   nodeResolve: true,
+  browsers: [],
 };