chore: add comment + altered test

packages/abi-coder/src/encoding/coders/BigNumberCoder.test.ts

@@ -33,10 +33,19 @@ describe('BigNumberCoder', () => {
     expect(data).toEqual(expected);
   });
 
+  it('should throw an error when encoding [number more than max safe integer]', () => {
+    const coder = new BigNumberCoder('u64');
+    const value: number = Number.MAX_SAFE_INTEGER + 1;
+
+    expect(() => coder.encode(value)).toThrow(
+      new FuelError(ErrorCode.ENCODE_ERROR, 'Invalid u64 type - number value is too large.')
+    );
+  });
+
   it('should encode a u64 [very big number - as string]', () => {
     const coder = new BigNumberCoder('u64');
-    const value: string = (Number.MAX_SAFE_INTEGER + 1).toString();
-    const expected = new Uint8Array([0, 32, 0, 0, 0, 0, 0, 0]);
+    const value: string = '76472027892439376';
+    const expected = new Uint8Array([1, 15, 174, 231, 121, 200, 89, 80]);
 
     const data = coder.encode(value);
 
@@ -45,7 +54,7 @@ describe('BigNumberCoder', () => {
 
   it('should throw an error when encoding [number more than max safe integer]', () => {
     const coder = new BigNumberCoder('u64');
-    const value: number = Number.MAX_SAFE_INTEGER + 1;
+    const value: number = 76472027892439376;
 
     expect(() => coder.encode(value)).toThrow(
       new FuelError(ErrorCode.ENCODE_ERROR, 'Invalid u64 type - number value is too large.')

packages/abi-coder/src/encoding/coders/BigNumberCoder.ts

@@ -20,6 +20,9 @@ export class BigNumberCoder extends Coder<BNInput, BN> {
   encode(value: BNInput): Uint8Array {
     let bytes;
 
+    // We throw an error if the value is a number and it's more than the max safe integer
+    // This is because we can experience some odd behavior with integers more than the max safe integer
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER#description
     if (typeof value === 'number' && value > Number.MAX_SAFE_INTEGER) {
       throw new FuelError(
         ErrorCode.ENCODE_ERROR,