Testing API

The Deno language server supports a custom set of APIs to enable testing. These are built around providing information to enable the vscode's Testing API but can be used by other language server clients to provide a similar interface.


Both the client and the server should support the experimental testingApi capability:

interface ClientCapabilities {
  experimental?: {
    testingApi: boolean;
interface ServerCapabilities {
  experimental?: {
    testingApi: boolean;

When a version of Deno that supports the testing API encounters a client which supports the capability, it will initialize the code which handles the test detection and will start providing the notifications which enable it.

It should also be noted that when the testing API capabilities are enabled, the testing code lenses will no longer be sent to the client.


There are specific settings which change the behavior of the language server:


The server will send notifications to the client under certain conditions.


When a module containing tests is discovered by the server, it will notify the client by sending a deno/testModule notification along with a payload of TestModuleParams.

Deno structures in this fashion:

When Deno does static analysis of a test module, it attempts to identify any tests and test steps. Because of the dynamic way tests can be declared in Deno, they cannot always be statically identified and can only be identified when the module is executed. The notification is designed to handle both of these situations when updating the client. When tests are discovered statically, the notification kind will be "replace", when tests or steps are discovered at execution time, the notification kind will be "insert".

As a test document is edited in the editor, and textDocument/didChange notifications are received from the client, the static analysis of those changes will be performed server side and if the tests have changed, the client will receive a notification.

When a client receives a "replace" notification, it can safely "replace" a test module representation, where when an "insert" it received, it should recursively try to add to existing representations.

For test modules the textDocument.uri should be used as the unique ID for any representation (as it the string URL to the unique module). TestData items contain a unique id string. This id string is a SHA-256 hash of identifying information that the server tracks for a test.

interface TestData {
  /** The unique ID for this test/step. */
  id: string;

  /** The display label for the test/step. */
  label: string;

  /** Any test steps that are associated with this test/step */
  steps?: TestData[];

  /** The range of the owning text document that applies to the test. */
  range?: Range;

interface TestModuleParams {
  /** The text document identifier that the tests are related to. */
  textDocument: TextDocumentIdentifier;

  /** A indication if tests described are _newly_ discovered and should be
   * _inserted_ or if the tests associated are a replacement for any existing
   * tests. */
  kind: "insert" | "replace";

  /** The text label for the test module. */
  label: string;

  /** An array of tests that are owned by this test module. */
  tests: TestData[];


When a test module is deleted that the server is observing, the server will issue a deno/testModuleDelete notification. When receiving the notification the client should remove the representation of the test module and all of its children tests and test steps.

interface TestModuleDeleteParams {
  /** The text document identifier that has been removed. */
  textDocument: TextDocumentIdentifier;


When a deno/testRun is requested from the client, the server will support progress of that test run via the deno/testRunProgress notification.

The client should process these messages and update any UI representation.

The state change is represented in the .message.kind property of the TestRunProgressParams. The states are:

interface TestIdentifier {
  /** The test module the message is related to. */
  textDocument: TextDocumentIdentifier;

  /** The optional ID of the test. If not present, then the message applies to
   * all tests in the test module. */
  id?: string;

  /** The optional ID of the step. If not present, then the message only applies
   * to the test. */
  stepId?: string;

interface TestMessage {
  /** The content of the message. */
  message: MarkupContent;

  /** An optional string which represents the expected output. */
  expectedOutput?: string;

  /** An optional string which represents the actual output. */
  actualOutput?: string;

  /** An optional location related to the message. */
  location?: Location;

interface TestEnqueuedStartedSkipped {
  /** The state change that has occurred to a specific test or test step.
   * - `"enqueued"` - the test is now enqueued to be tested
   * - `"started"` - the test has started
   * - `"skipped"` - the test was skipped
  type: "enqueued" | "started" | "skipped";

  /** The test or test step relating to the state change. */
  test: TestIdentifier;

interface TestFailedErrored {
  /** The state change that has occurred to a specific test or test step.
   * - `"failed"` - The test failed to run properly, versus the test erroring.
   *   currently the Deno language server does not support this.
   * - `"errored"` - The test errored.
  type: "failed" | "errored";

  /** The test or test step relating to the state change. */
  test: TestIdentifier;

  /** Messages related to the state change. */
  messages: TestMessage[];

  /** An optional duration, in milliseconds from the start to the current
   * state. */
  duration?: number;

interface TestPassed {
  /** The state change that has occurred to a specific test or test step. */
  type: "passed";

  /** The test or test step relating to the state change. */
  test: TestIdentifier;

  /** An optional duration, in milliseconds from the start to the current
   * state. */
  duration?: number;

interface TestOutput {
  /** The test or test step has output information / logged information. */
  type: "output";

  /** The value of the output. */
  value: string;

  /** The associated test or test step if there was one. */
  test?: TestIdentifier;

  /** An optional location associated with the output. */
  location?: Location;

interface TestEnd {
  /** The test run has ended. */
  type: "end";

type TestRunProgressMessage =
  | TestEnqueuedStartedSkipped
  | TestFailedErrored
  | TestPassed
  | TestOutput
  | TestEnd;

interface TestRunProgressParams {
  /** The test run ID that the progress message applies to. */
  id: number;

  /** The message*/
  message: TestRunProgressMessage;


The server handles two different requests:


To request the language server to perform a set of tests, the client sends a deno/testRun request, which includes that ID of the test run to be used in future responses to the client, the type of the test run, and any test modules or tests to include or exclude.

Currently Deno only supports the "run" kind of test run. Both "debug" and "coverage" are planned to be supported in the future.

When there are no test modules or tests that are included, it implies that all discovered tests modules and tests should be executed. When a test module is included, but not any test ids, it implies that all tests within that test module should be included. Once all the tests are identified, any excluded tests are removed and the resolved set of tests are returned in the response as "enqueued".

It is not possible to include or exclude test steps via this API, because of the dynamic nature of how test steps are declared and run.

interface TestRunRequestParams {
  /** The id of the test run to be used for future messages. */
  id: number;

  /** The run kind. Currently Deno only supports `"run"` */
  kind: "run" | "coverage" | "debug";

  /** Test modules or tests to exclude from the test run. */
  exclude?: TestIdentifier[];

  /** Test modules or tests to include in the test run. */
  include?: TestIdentifier[];

interface EnqueuedTestModule {
  /** The test module the enqueued test IDs relate to */
  textDocument: TextDocumentIdentifier;

  /** The test IDs which are now enqueued for testing */
  ids: string[];

interface TestRunResponseParams {
  /** Test modules and test IDs that are now enqueued for testing. */
  enqueued: EnqueuedTestModule[];


If a client wishes to cancel a currently running test run, it sends a deno/testRunCancel request with the test ID to cancel. The response back will be a boolean of true if the test is cancelled or false if it was not possible. Appropriate test progress notifications will still be sent as the test is being cancelled.

interface TestRunCancelParams {
  /** The test id to be cancelled. */
  id: number;