add test to check printer idempotence

packages/babel-plugin-relay/__tests__/printGraphQL-test.js

@@ -0,0 +1,59 @@
+/**
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+const print = require('../printGraphQL');
+
+const { parse } = require('graphql');
+const path = require('path');
+const fs = require('fs');
+
+type OutputFixture = { name: string, input: string, output: string };
+type ErrorFixture = { name: string, input: string, error: string };
+type PrinterFixture = OutputFixture | ErrorFixture;
+
+describe('printGraphQL', () => {
+  const outputFixtures = loadPrinterFixtures()
+    .filter(fixture => fixture.output)
+    // object key format doesn't work
+    .map(fixture => [fixture.name, fixture.input, fixture.output]);
+
+  it.each(outputFixtures)('tests printer idempotence: %s', (_name, input, expected) => {
+    expect(print(parse(input))).toEqual(expected);
+  });
+});
+
+function loadPrinterFixtures(): PrinterFixture[] {
+  const fixturesPath = path.join(
+    __dirname,
+    '../../../compiler/crates/graphql-text-printer/tests/print_ast/fixtures',
+  );
+  const fixtures = [];
+  for (const file of fs.readdirSync(fixturesPath)) {
+    if (!file.endsWith('.expected')) {
+      continue;
+    }
+    const content = fs.readFileSync(path.join(fixturesPath, file), 'utf8');
+    try {
+      const fixture = parsePrintFixture(file, content);
+      fixtures.push(fixture);
+    } catch (err) {
+      console.error(err, `\n\nFailed to parse ${file}`);
+    }
+  }
+  return fixtures;
+}
+
+function parsePrintFixture(name: string, content: string): PrinterFixture {
+  const successPatttern = /^=+ INPUT =+\n(?<input>[\s\S]*)\n=+ OUTPUT =+\n(?<output>[\s\S]*)$/;
+  const failurePattern = /^=+ INPUT =+\n(?<input>[\s\S]*)\n=+ ERROR =+\n(?<error>[\s\S]*)$/;
+
+  const match = content.match(successPatttern) ?? content.match(failurePattern);
+  if (!match) {
+    throw new Error('Unknown fixture format from the graphql-text-printer crate!');
+  }
+  return { name, ...match.groups } as PrinterFixture;
+}