Add tests for loadGetInitialProps

test/unit/loadGetInitialProps.test.js

@@ -0,0 +1,52 @@
+/* global describe, it, expect */
+import { loadGetInitialProps } from '../../dist/lib/utils'
+
+describe('loadGetInitialProps', () => {
+  it('should throw if getInitialProps is defined as an instance method', () => {
+    class TestComponent {
+      getInitialProps () {}
+    }
+    const rejectPromise = loadGetInitialProps(TestComponent, {})
+    const error = new Error('"TestComponent.getInitialProps()" is defined as an instance method - visit https://err.sh/next.js/get-inital-props-as-an-instance-method for more information.')
+    return expect(rejectPromise).rejects.toEqual(error)
+  })
+
+  it('should resolve to an object if getInitialProps is missing', async () => {
+    const result = await loadGetInitialProps(() => {}, {})
+    expect(result).toEqual({})
+  })
+
+  it('should resolve getInitialProps', async () => {
+    class TestComponent {
+      static async getInitialProps () {
+        return { foo: 1 }
+      }
+    }
+    const result = await loadGetInitialProps(TestComponent, {})
+    expect(result).toEqual({ foo: 1 })
+  })
+
+  it('should be able to return an invalid value if the request was already sent', async () => {
+    class TestComponent {
+      static async getInitialProps () {
+        return 'invalidValue'
+      }
+    }
+    const ctx = {
+      res: {
+        finished: true
+      }
+    }
+    const result = await loadGetInitialProps(TestComponent, ctx)
+    expect(result).toBe('invalidValue')
+  })
+
+  it('should throw if getInitialProps won\'t return an object ', () => {
+    class TestComponent {
+      static async getInitialProps () {}
+    }
+    const rejectPromise = loadGetInitialProps(TestComponent, {})
+    const error = new Error('"TestComponent.getInitialProps()" should resolve to an object. But found "undefined" instead.')
+    return expect(rejectPromise).rejects.toEqual(error)
+  })
+})