Update Sampling Percentage to Accept 0 as Valid (#1337)

* Update setting of sampling ratio to accept 0.

* Add test for zero sampling.

* Update to a simple undefined check since the distro will handle full sampling ratio validity logic.

* Update to send warning if sampling percentage is set incorrectly in the app insights v3.

* Add test to ensure warning will be thrown.

src/shared/configuration/config.ts

@@ -109,7 +109,7 @@ export class ApplicationInsightsConfig {
                 options.instrumentationOptions
             );
             this.resource = Object.assign(this.resource, options.resource);
-            this.samplingRatio = options.samplingRatio || this.samplingRatio;
+            this.samplingRatio = options.samplingRatio !== undefined ? options.samplingRatio : this.samplingRatio;
 
             // Set console logging level from env var
             if (process.env[loggingLevel]) { 

src/shim/shim-config.ts

@@ -151,8 +151,12 @@ class Config implements IConfig {
             ...options.instrumentationOptions,
             console: { enabled: false },
         };
-        if (this.samplingPercentage) {
-            options.samplingRatio = this.samplingPercentage / 100;
+        const samplingRatio = this.samplingPercentage / 100;
+        if (samplingRatio >= 0 && samplingRatio <= 1) {
+            options.samplingRatio = samplingRatio;
+        } else {
+            options.samplingRatio = 1;
+            this._configWarnings.push("Sampling percentage should be between 0 and 100. Defaulting to 100.");
         }
         options.instrumentationOptions = {
             ...options.instrumentationOptions,

test/unitTests/shim/config.tests.ts

@@ -102,6 +102,15 @@ describe("shim/configuration/config", () => {
             assert.equal(options.azureMonitorExporterOptions.disableOfflineStorage, false, "wrong disableOfflineStorage");
         });
 
+        it("should initialize zero sampling percentage", () => {
+            const config = new Config(connectionString);
+            config.samplingPercentage = 0;
+
+            let options = config.parseConfig();
+
+            assert.equal(options.samplingRatio, 0, "wrong samplingRatio");
+        });
+
         it("should activate DEBUG internal logger", () => {
             const env = <{ [id: string]: string }>{};
             process.env = env;
@@ -201,6 +210,14 @@ describe("shim/configuration/config", () => {
             assert.equal(process.env["APPLICATION_INSIGHTS_NO_STANDARD_METRICS"], "disable");
         });
 
+        it("should warn if an invalid sampling percentage is passed in", () => {
+            const config = new Config(connectionString);
+            const warnings = config["_configWarnings"];
+            config.samplingPercentage = 101;
+            config.parseConfig();
+            assert.ok(checkWarnings("Sampling percentage should be between 0 and 100. Defaulting to 100.", warnings), "warning was not raised");
+        });
+
         describe("#Shim unsupported messages", () => {
             it("should warn if disableAppInsights is set", () => {
                 const config = new Config(connectionString);