fix: error from fill method should not be emitted

Fixes #2103

Author: surbhigarg92

src/session-pool.ts

@@ -783,11 +783,7 @@ export class SessionPool extends EventEmitter implements SessionPoolInterface {
       return;
     }
 
-    try {
-      await this._createSessions(needed);
-    } catch (e) {
-      this.emit('error', e);
-    }
+    await this._createSessions(needed);
   }
 
   /**
@@ -993,7 +989,24 @@ export class SessionPool extends EventEmitter implements SessionPoolInterface {
     const pings = sessions.map(session => this._ping(session));
 
     await Promise.all(pings);
-    return this._fill();
+    try {
+      await this._fill();
+    } catch (error) {
+      // Ignore `Database not found` error. This allows a user to call instance.database('db-name')
+      // for a database that does not yet exist with SessionPoolOptions.min > 0.
+      const err = error as ServiceError;
+      if (
+        isDatabaseNotFoundError(err) ||
+        isInstanceNotFoundError(err) ||
+        isCreateSessionPermissionError(err) ||
+        isDefaultCredentialsNotSetError(err) ||
+        isProjectIdNotSetInEnvironmentError(err)
+      ) {
+        return;
+      }
+      this.emit('error', err);
+    }
+    return;
   }
 
   /**

test/session-pool.ts

@@ -953,12 +953,10 @@ describe('SessionPool', () => {
 
       stub.rejects(error);
 
-      sessionPool.once('error', err => {
+      sessionPool._fill().catch(err => {
         assert.strictEqual(err, error);
         done();
       });
-
-      sessionPool._fill();
     });
   });
 
@@ -1286,6 +1284,23 @@ describe('SessionPool', () => {
 
       assert.strictEqual(fillStub.callCount, 1);
     });
+
+    it('should not throw error when database not found', async () => {
+      const fakeSessions = [createSession()];
+      sandbox.stub(sessionPool, '_getIdleSessions').returns(fakeSessions);
+
+      const error = {
+        code: grpc.status.NOT_FOUND,
+        message: 'Database not found',
+      } as grpc.ServiceError;
+      sandbox.stub(sessionPool, '_fill').rejects(error);
+
+      try {
+        await sessionPool._pingIdleSessions();
+      } catch (err) {
+        assert.ifError(err);
+      }
+    });
   });
 
   describe('_release', () => {