chore(tests): unit test read cache (#501)

packages/postgraphile-core/__tests__/unit/__snapshots__/read-cache.test.js.snap

@@ -0,0 +1,3 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`when cache file has invalid content, getPostGraphileBuilder should error 1`] = `[Error: Failed to parse cache file 'path/to/cache', perhaps it is corrupted? SyntaxError: Unexpected token h in JSON at position 1]`;

packages/postgraphile-core/__tests__/unit/read-cache.test.js

@@ -0,0 +1,88 @@
+const fs = require("fs");
+const graphileBuild = require("graphile-build");
+const { getPostGraphileBuilder } = require("../..");
+
+jest.mock("fs");
+jest.mock("graphile-build");
+
+beforeEach(() => {
+  // required for mocks assertions
+  jest.resetAllMocks();
+});
+
+/*
+
+Current behaviour of getPostGraphileBuilder and readCache option:
+
+1. cacheString is loaded by reading the file defined by readCache
+2. memoizeCache is set by JSON.parse(cacheString)
+3. persistentMemoizeWithKey is a function created dynamically that will use memoizeCache
+4. getBuilder(imported from graphile-build) is called, passing persistentMemoizeWithKey as one of the arguments
+
+Test strategy for readCache
+
+1. Mock fs.readFile to control input
+2. Mock getBuilder to control output
+3. Test different inputs and validate that getBuilder is called with expected output
+
+*/
+
+test("when cache file has content, persistentMemoizeWithKey should be a valid function", async () => {
+  // mock fs.readFile to return an object
+  fs.readFile.mockImplementationOnce((path, options, cb) =>
+    cb(null, '{ "__test": true }')
+  );
+
+  // mock getBuilder to fake output
+  const expectedOutput = {};
+  graphileBuild.getBuilder.mockResolvedValueOnce(expectedOutput);
+  // call our method and test output
+  const output = await getPostGraphileBuilder({}, [], {
+    readCache: "path/to/cache",
+  });
+  expect(output).toBe(expectedOutput);
+  expect(fs.readFile).toHaveBeenCalledTimes(1);
+  expect(graphileBuild.getBuilder).toHaveBeenCalledTimes(1);
+  // check persistentMemoizeWithKey, the actual "result" of readCache flag
+  const {
+    persistentMemoizeWithKey,
+  } = graphileBuild.getBuilder.mock.calls[0][1];
+  expect(typeof persistentMemoizeWithKey).toBe("function");
+  expect(persistentMemoizeWithKey("__test")).toEqual(true);
+  expect(() => persistentMemoizeWithKey("unknown_key")).toThrow();
+});
+
+test("when no readCache flag, persistentMemoizeWithKey should be undefined", async () => {
+  // mock getBuilder to fake output
+  const expectedOutput = {};
+  graphileBuild.getBuilder.mockResolvedValueOnce(expectedOutput);
+  // call our method and test output
+  const output = await getPostGraphileBuilder({}, [], {});
+  expect(output).toBe(expectedOutput);
+  expect(graphileBuild.getBuilder).toHaveBeenCalledTimes(1);
+  // check persistentMemoizeWithKey, the actual "result" of readCache flag
+  const {
+    persistentMemoizeWithKey,
+  } = graphileBuild.getBuilder.mock.calls[0][1];
+  expect(persistentMemoizeWithKey).toBeUndefined();
+});
+
+test("when cache file has invalid content, getPostGraphileBuilder should error", async () => {
+  // mock fs.readFile to return an object
+  fs.readFile.mockImplementationOnce((path, options, cb) =>
+    cb(null, "thisisnotjson")
+  );
+
+  // call our method and check error
+
+  let error;
+  try {
+    await getPostGraphileBuilder({}, [], {
+      readCache: "path/to/cache",
+    });
+  } catch (e) {
+    error = e;
+  }
+  expect(error).toMatchSnapshot();
+  expect(fs.readFile).toHaveBeenCalledTimes(1);
+});

packages/postgraphile-core/src/index.ts

@@ -183,7 +183,7 @@ const awaitKeys = async (obj: { [key: string]: Promise<any> }) => {
   return result;
 };
 
-const getPostGraphileBuilder = async (
+export const getPostGraphileBuilder = async (
   pgConfig: PgConfig,
   schemas: string | Array<string>,
   options: PostGraphileCoreOptions = {}