Add support for bigint to pretty-format

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Fixes
 
+- `[pretty-format]` Print `BigInt` as a readable number instead of `{}` [#8138](https://github.com/facebook/jest/pull/8138)
+
 ### Chore & Maintenance
 
 - `[*]` Remove flow from code base ([#8061](https://github.com/facebook/jest/pull/8061))

packages/pretty-format/src/__tests__/prettyFormat.test.ts

@@ -224,6 +224,29 @@ describe('prettyFormat()', () => {
     expect(prettyFormat(val)).toEqual('-0');
   });
 
+  /* global BigInt */
+  if (typeof BigInt === 'function') {
+    it('prints a positive bigint', () => {
+      const val = BigInt(123);
+      expect(prettyFormat(val)).toEqual('123n');
+    });
+
+    it('prints a negative bigint', () => {
+      const val = BigInt(-123);
+      expect(prettyFormat(val)).toEqual('-123n');
+    });
+
+    it('prints zero bigint', () => {
+      const val = BigInt(0);
+      expect(prettyFormat(val)).toEqual('0n');
+    });
+
+    it('prints negative zero bigint', () => {
+      const val = BigInt(-0);
+      expect(prettyFormat(val)).toEqual('0n');
+    });
+  }
+
   it('prints a date', () => {
     const val = new Date(10e11);
     expect(prettyFormat(val)).toEqual('2001-09-09T01:46:40.000Z');

packages/pretty-format/src/index.ts

@@ -72,6 +72,10 @@ function printNumber(val: number): string {
   return Object.is(val, -0) ? '-0' : String(val);
 }
 
+function printBigInt(val: bigint): string {
+  return String(`${val}n`);
+}
+
 function printFunction(val: Function, printFunctionName: boolean): string {
   if (!printFunctionName) {
     return '[Function]';
@@ -112,6 +116,9 @@ function printBasicValue(
   if (typeOf === 'number') {
     return printNumber(val);
   }
+  if (typeOf === 'bigint') {
+    return printBigInt(val);
+  }
   if (typeOf === 'string') {
     if (escapeString) {
       return '"' + val.replace(/"|\\/g, '\\$&') + '"';