Test plugins: Add datasource test plugin with field tests (#95472)

* add new test plugin

* add some field validation tests

* update lockfile

* fix bad test file name

e2e/test-plugins/grafana-test-datasource/datasource.ts

@@ -0,0 +1,93 @@
+import { getBackendSrv, isFetchError } from '@grafana/runtime';
+import {
+  CoreApp,
+  DataQueryRequest,
+  DataQueryResponse,
+  DataSourceApi,
+  DataSourceInstanceSettings,
+  createDataFrame,
+  FieldType,
+} from '@grafana/data';
+
+import { MyQuery, MyDataSourceOptions, DEFAULT_QUERY, DataSourceResponse } from './types';
+import { lastValueFrom } from 'rxjs';
+
+export class DataSource extends DataSourceApi<MyQuery, MyDataSourceOptions> {
+  baseUrl: string;
+
+  constructor(instanceSettings: DataSourceInstanceSettings<MyDataSourceOptions>) {
+    super(instanceSettings);
+    this.baseUrl = instanceSettings.url!;
+  }
+
+  getDefaultQuery(_: CoreApp): Partial<MyQuery> {
+    return DEFAULT_QUERY;
+  }
+
+  filterQuery(query: MyQuery): boolean {
+    // if no query has been provided, prevent the query from being executed
+    return !!query.queryText;
+  }
+
+  async query(options: DataQueryRequest<MyQuery>): Promise<DataQueryResponse> {
+    const { range } = options;
+    const from = range!.from.valueOf();
+    const to = range!.to.valueOf();
+
+    // Return a constant for each query.
+    const data = options.targets.map((target) => {
+      return createDataFrame({
+        refId: target.refId,
+        fields: [
+          { name: 'Time', values: [from, to], type: FieldType.time },
+          { name: 'Value', values: [target.constant, target.constant], type: FieldType.number },
+        ],
+      });
+    });
+
+    return { data };
+  }
+
+  async request(url: string, params?: string) {
+    const response = getBackendSrv().fetch<DataSourceResponse>({
+      url: `${this.baseUrl}${url}${params?.length ? `?${params}` : ''}`,
+    });
+    return lastValueFrom(response);
+  }
+
+  /**
+   * Checks whether we can connect to the API.
+   */
+  async testDatasource() {
+    const defaultErrorMessage = 'Cannot connect to API';
+
+    try {
+      const response = await this.request('/health');
+      if (response.status === 200) {
+        return {
+          status: 'success',
+          message: 'Success',
+        };
+      } else {
+        return {
+          status: 'error',
+          message: response.statusText ? response.statusText : defaultErrorMessage,
+        };
+      }
+    } catch (err) {
+      let message = '';
+      if (typeof err === 'string') {
+        message = err;
+      } else if (isFetchError(err)) {
+        message = 'Fetch error: ' + (err.statusText ? err.statusText : defaultErrorMessage);
+        if (err.data && err.data.error && err.data.error.code) {
+          message += ': ' + err.data.error.code + '. ' + err.data.error.message;
+        }
+      }
+      return {
+        status: 'error',
+        message,
+      };
+    }
+  }
+}