From 5220f9be8a24e84121170b910bcda9860e79d5d3 Mon Sep 17 00:00:00 2001
From: Kelvin Jin <kelvinjin@google.com>
Date: Mon, 29 Oct 2018 10:43:52 -0700
Subject: [PATCH]  fix: allow sampling rate to be less than 1 (#896)

---
 src/tracing-policy.ts     |  2 +-
 test/test-trace-policy.ts | 37 ++++++++++++++++++++++++++++++++-----
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/src/tracing-policy.ts b/src/tracing-policy.ts
index 9236950a9..cc8422abf 100644
--- a/src/tracing-policy.ts
+++ b/src/tracing-policy.ts
@@ -76,7 +76,7 @@ export class TracePolicy {
    * @param config Configuration for the TracePolicy instance.
    */
   constructor(config: TracePolicyConfig) {
-    if (config.samplingRate >= 0 && config.samplingRate < 1) {
+    if (config.samplingRate === 0) {
       this.sampler = {shouldTrace: () => true};
     } else if (config.samplingRate < 0) {
       this.sampler = {shouldTrace: () => false};
diff --git a/test/test-trace-policy.ts b/test/test-trace-policy.ts
index e2aa08e7e..a9e2e0a07 100644
--- a/test/test-trace-policy.ts
+++ b/test/test-trace-policy.ts
@@ -35,14 +35,17 @@ describe('TracePolicy', () => {
   });
 
   describe('Sampling', () => {
-    const tracesPerSecond = [10, 50, 150, 200, 500, 1000];
-    for (const expected of tracesPerSecond) {
-      it(`should throttle traces when samplingRate = ` + expected, () => {
+    const NUM_SECONDS = 10;
+    const testCases = [0.1, 0.5, 1, 10, 50, 150, 200, 500, 1000];
+    for (const testCase of testCases) {
+      it(`should throttle traces when samplingRate = ` + testCase, () => {
         const policy =
-            new TracePolicy({samplingRate: expected, ignoreUrls: []});
+            new TracePolicy({samplingRate: testCase, ignoreUrls: []});
+        const expected = NUM_SECONDS * testCase;
         let actual = 0;
         const start = Date.now();
-        for (let timestamp = start; timestamp < start + 1000; timestamp++) {
+        for (let timestamp = start; timestamp < start + 1000 * NUM_SECONDS;
+             timestamp++) {
           if (policy.shouldTrace({timestamp, url: ''})) {
             actual++;
           }
@@ -55,5 +58,29 @@ describe('TracePolicy', () => {
             `Expected close to (>=0.8*) ${expected} traced but got ${actual}`);
       });
     }
+
+    it('should always sample when samplingRate = 0', () => {
+      const policy = new TracePolicy({samplingRate: 0, ignoreUrls: []});
+      let numSamples = 0;
+      const start = Date.now();
+      for (let timestamp = start; timestamp < start + 1000; timestamp++) {
+        if (policy.shouldTrace({timestamp, url: ''})) {
+          numSamples++;
+        }
+      }
+      assert.strictEqual(numSamples, 1000);
+    });
+
+    it('should never sample when samplingRate < 0', () => {
+      const policy = new TracePolicy({samplingRate: -1, ignoreUrls: []});
+      let numSamples = 0;
+      const start = Date.now();
+      for (let timestamp = start; timestamp < start + 1000; timestamp++) {
+        if (policy.shouldTrace({timestamp, url: ''})) {
+          numSamples++;
+        }
+      }
+      assert.strictEqual(numSamples, 0);
+    });
   });
 });