Fix race conditions in Chrome coverage collection (#2715)
Fixes race conditions causing intermittent empty coverage results in
chrome tests (such as in `coverage_test.dart`).
- in `browsermanager`: await `_environment` during startup before
completing initialization. this ensures the devtools connection and
profiler are ready before test suites begin executing.
- in `chrome`:
- register the `onscriptparsed` listener before calling
`tabconnection.debugger.enable()` to avoid dropping initial
`debugger.scriptparsed` events emitted during initialization.
- establish the remote debugger url and tab connection together in
`_connect`, returning both as a record.
- safely handle null tab connections in `gathercoverage`.
Welcome! package:test is the standard testing library for Dart and Flutter. If you have questions about Dart testing, please see the docs for package:test. package:test_api and package:test_core are implementation details and generally not user-facing.
package:checks is a relatively new library for expressing test expectations. It's a more modern version of package:matcher and features a literate API.
| Package | Description | Issues | Version |
|---|---|---|---|
| checks | A framework for checking values against expectations and building custom expectations. |  |  |
| fake_async | Fake asynchronous events such as timers and microtasks for deterministic testing. | |  |
| matcher | Support for specifying test expectations via an extensible Matcher class. Also includes a number of built-in Matcher implementations for common cases. | |  |
| test | A full featured library for writing and running Dart tests across platforms. | |  |
| test_api | The user facing API for structuring Dart tests and checking expectations. |  | |
| test_core | A basic library for writing tests and running them on the VM. |  | |
| test_descriptor | An API for defining and verifying files and directory structures. | |  |
| test_process | Test processes: starting; validating stdout and stderr; checking exit code. | |  |