Throw error if serviceName is not provided

Signed-off-by: Won Jun Jang <wjang@uber.com>

src/configuration.js

@@ -173,6 +173,10 @@ export default class Configuration {
             );
         }
 
+        if (config.serviceName === undefined || config.serviceName === null) {
+            throw new Error(`config.serviceName must be provided`);
+        }
+
         return new Tracer(
             config.serviceName,
             reporter,

test/init_tracer.js

@@ -33,6 +33,10 @@ describe('initTracer', () => {
         expect(tracer).to.be.an.instanceof(opentracing.Tracer);
     });
 
+    it ('should throw error on invalid serviceName', () => {
+        expect(() => { initTracer({}); }).to.throw('config.serviceName must be provided');
+    });
+
     it ('should initialize normal tracer when only service name given', () => {
         let config = {
             serviceName: 'test-service'
@@ -44,10 +48,10 @@ describe('initTracer', () => {
     });
 
     it ('should initialize proper samplers', () => {
-        var config = {
+        let config = {
             serviceName: 'test-service'
         };
-        var options = [
+        let options = [
             { type: 'const', param: 1, expectedType: ConstSampler, expectedParam: 1 },
             { type: 'ratelimiting', param: 2, expectedType: RateLimitingSampler, expectedParam: 2 },
             { type: 'probabilistic', param: 0.5, expectedType: ProbabilisticSampler, expectedParam: 0.5 },
@@ -69,10 +73,10 @@ describe('initTracer', () => {
     });
 
     it ('should throw error on sampler incorrect type', () => {
-        var config = {
+        let config = {
             serviceName: 'test-service'
         };
-        var options = [
+        let options = [
             { type: 'const', param: 'bad-value' },
             { type: 'ratelimiting', param: 'bad-value' },
             { type: 'probabilistic', param: 'bad-value' },
@@ -108,7 +112,7 @@ describe('initTracer', () => {
                 agentPort: 4939,
                 flushIntervalMs: 2000
             }
-        }
+        };
         let tracer = initTracer(config);
 
         expect(tracer._reporter).to.be.an.instanceof(CompositeReporter);
@@ -127,10 +131,10 @@ describe('initTracer', () => {
     });
 
     it ('should pass options to tracer', () => {
-        var logger = {
+        let logger = {
             'info': function info(msg){}
         };
-        var metrics = {
+        let metrics = {
             'createCounter': function createCounter() { return {}; },
             'createGauge': function createGauge() { return {}; },
             'createTimer': function createTimer() { return {}; },