Use default FACTORY_ADDRESS if the chain is not in the map (#160)

* Use default FACTORY_ADDRESS if the chain is not in the map

* Fix code style issues with Prettier

* test

* conflict

* Fix code style issues with Prettier

---------
Co-authored-by: Lint Action <lint-action@samuelmeuli.com>

src/entities/pair.test.ts

+import { BigNumber } from '@ethersproject/bignumber'
 import { ChainId, CurrencyAmount, Price, Token, WETH9 } from '@uniswap/sdk-core'
+import { FACTORY_ADDRESS } from '../constants'
 import { InsufficientInputAmountError } from '../errors'
 import { computePairAddress, Pair } from './pair'
-import { BigNumber } from '@ethersproject/bignumber'
 
 describe('computePairAddress', () => {
   it('should correctly compute the pool address', () => {
@@ -42,6 +43,9 @@ describe('Pair', () => {
   const USDC = new Token(1, '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', 18, 'USDC', 'USD Coin')
   const DAI = new Token(1, '0x6B175474E89094C44Da98b954EedeAC495271d0F', 18, 'DAI', 'DAI Stablecoin')
 
+  const USDC_SEPOLIA = new Token(11155111, '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', 18, 'USDC', 'USD Coin')
+  const DAI_SEPOLIA = new Token(11155111, '0x6B175474E89094C44Da98b954EedeAC495271d0F', 18, 'DAI', 'DAI Stablecoin')
+
   describe('constructor', () => {
     it('cannot be used for tokens on different chains', () => {
       expect(
@@ -54,6 +58,10 @@ describe('Pair', () => {
     it('returns the correct address', () => {
       expect(Pair.getAddress(USDC, DAI)).toEqual('0xAE461cA67B15dc8dc81CE7615e0320dA1A9aB8D5')
     })
+
+    it('returns the default address for a testnet not in the map', () => {
+      expect(Pair.getAddress(USDC_SEPOLIA, DAI_SEPOLIA)).toEqual(FACTORY_ADDRESS)
+    })
   })
 
   describe('#token0', () => {

src/entities/pair.ts

-import { BigintIsh, Price, sqrt, Token, CurrencyAmount, Percent } from '@uniswap/sdk-core'
-import invariant from 'tiny-invariant'
-import JSBI from 'jsbi'
-import { pack, keccak256 } from '@ethersproject/solidity'
 import { getCreate2Address } from '@ethersproject/address'
 import { BigNumber } from '@ethersproject/bignumber'
+import { keccak256, pack } from '@ethersproject/solidity'
+import { BigintIsh, CurrencyAmount, Percent, Price, sqrt, Token } from '@uniswap/sdk-core'
+import JSBI from 'jsbi'
+import invariant from 'tiny-invariant'
 
 import {
+  _1000,
+  _997,
+  BASIS_POINTS,
+  FACTORY_ADDRESS,
   FACTORY_ADDRESS_MAP,
+  FIVE,
   INIT_CODE_HASH,
   MINIMUM_LIQUIDITY,
-  FIVE,
-  _997,
-  _1000,
   ONE,
-  ZERO,
-  BASIS_POINTS,
   ONE_HUNDRED_PERCENT,
+  ZERO,
   ZERO_PERCENT
 } from '../constants'
-import { InsufficientReservesError, InsufficientInputAmountError } from '../errors'
+import { InsufficientInputAmountError, InsufficientReservesError } from '../errors'
 
 export const computePairAddress = ({
   factoryAddress,
@@ -41,7 +42,8 @@ export class Pair {
   private readonly tokenAmounts: [CurrencyAmount<Token>, CurrencyAmount<Token>]
 
   public static getAddress(tokenA: Token, tokenB: Token): string {
-    return computePairAddress({ factoryAddress: FACTORY_ADDRESS_MAP[tokenA.chainId], tokenA, tokenB })
+    const factoryAddress = FACTORY_ADDRESS_MAP[tokenA.chainId] ?? FACTORY_ADDRESS
+    return computePairAddress({ factoryAddress, tokenA, tokenB })
   }
 
   public constructor(currencyAmountA: CurrencyAmount<Token>, tokenAmountB: CurrencyAmount<Token>) {