Throw error if only one of host or port are defined

Author: dlarocque

packages/rules-unit-testing/src/impl/discovery.ts

@@ -87,16 +87,23 @@ export function getEmulatorHostAndPort(
   conf?: EmulatorConfig,
   discovered?: DiscoveredEmulators
 ) {
-  if (conf && 'host' in conf && 'port' in conf) {
+  if (conf && ('host' in conf || 'port' in conf)) {
+    const { host, port } = conf as any;
+    if (!host || !port) {
+      throw new Error(
+        `Invalid configuration ${emulator}.host=${host} and ${emulator}.port=${port}. ` +
+          'If either parameter is supplied, both must be defined.'
+      );
+    }
     if (discovered && !discovered[emulator]) {
       console.warn(
         `Warning: config for the ${emulator} emulator is specified, but the Emulator hub ` +
           'reports it as not running. This may lead to errors such as connection refused.'
       );
     }
     return {
-      host: fixHostname(conf.host, discovered?.hub?.host),
-      port: conf.port
+      host: fixHostname(host, discovered?.hub?.host),
+      port: port
     };
   }
   const envVar = EMULATOR_HOST_ENV_VARS[emulator];

packages/rules-unit-testing/test/impl/discovery.test.ts

@@ -140,6 +140,22 @@ describe('getEmulatorHostAndPort()', () => {
       expect(result?.host).to.equal('::1');
     });
 
+    it('throws if only host is present', async () => {
+      expect(() =>
+        getEmulatorHostAndPort('hub', {
+          host: '[::1]'
+        } as HostAndPort)
+      ).to.throw(/hub.port=undefined/);
+    });
+
+    it('throws if only port is present', async () => {
+      expect(() =>
+        getEmulatorHostAndPort('database', {
+          port: 1234
+        } as HostAndPort)
+      ).to.throw(/Invalid configuration database.host=undefined/);
+    });
+
     it('uses discovered host/port if both config and env var are unset', async () => {
       const result = getEmulatorHostAndPort('hub', undefined, {
         hub: { host: '::1', port: 3333 }