Make BN matchers compatible with chai's lengthOf

waffle-chai/src/matchers/bigNumber.ts

@@ -42,6 +42,10 @@ function overwriteBigNumberFunction(
   return function (this: Chai.AssertionStatic, ...args: any[]) {
     const [actual] = args;
     const expected = chaiUtils.flag(this, 'object');
+    if (chaiUtils.flag(this, 'doLength') && BigNumber.isBigNumber(actual)) {
+      _super.apply(this, [actual.toNumber()]);
+      return;
+    }
     if (BigNumber.isBigNumber(expected) || BigNumber.isBigNumber(actual)) {
       this.assert(
         BigNumber.from(expected)[functionName](actual),

waffle-chai/test/matchers/misc.test.ts

@@ -1,4 +1,5 @@
 import {expect, AssertionError} from 'chai';
+import {ethers} from 'ethers';
 
 describe('UNIT: Miscellaneous', () => {
   describe('Proper address', () => {
@@ -80,4 +81,20 @@ describe('UNIT: Miscellaneous', () => {
       ).to.throw(AssertionError, 'Expected "0x70" not to be a proper hex of length 2, but it was');
     });
   });
+
+  describe('Other chai matchers compatibility', () => {
+    it('lengthOf works', async () => {
+      const one = ethers.constants.One;
+      const list = [1, 2, 3];
+
+      expect(one).to.be.at.least(1);
+
+      expect(list.length).to.be.at.least(one);
+      expect(list).to.have.lengthOf.at.least(1);
+      expect([1]).to.have.lengthOf.at.least(one);
+      expect(list).to.have.lengthOf.at.least(one);
+      expect(list).to.have.lengthOf.at.most(one.mul(3));
+      expect(() => expect(list).to.have.lengthOf.at.most(one)).to.throw;
+    });
+  });
 });