fix(medusa, medusa-js): Use price selection strategy for GET /admin/variants (#2270)

**What**
- Adds the use of price selection strategy to the endpoint `GET /admin/variants`
- Updates medusa-js to reflect this change (expanding the parameters).

**Testing**
- Adds a new integration test validating that returned variants are now of type PricedVariant, with the expected fields: original_price, calculated_price, etc.

**Why**
- Our current RMA flows (in our admin dashboard) relied heavily on simply using `order.tax_rate` to calculate variant prices in the different RMA menus. As taxes in Medusa, have become feature complete this approach had become very naive and has several potential issues. Moving the responsibility for calculating the correct prices guarantees that we always show the correct prices to admins.

integration-tests/api/__tests__/admin/variant.js

@@ -3,9 +3,12 @@ const path = require("path")
 const setupServer = require("../../../helpers/setup-server")
 const { useApi } = require("../../../helpers/use-api")
 const { initDb, useDb } = require("../../../helpers/use-db")
+const { simpleProductFactory } = require("../../factories")
 
 const adminSeeder = require("../../helpers/admin-seeder")
+const adminVariantsSeeder = require("../../helpers/admin-variants-seeder")
 const productSeeder = require("../../helpers/product-seeder")
+const storeProductSeeder = require("../../helpers/store-product-seeder")
 
 jest.setTimeout(30000)
 
@@ -117,6 +120,7 @@ describe("/admin/products", () => {
 
     it("lists all product variants matching a specific product title", async () => {
       const api = useApi()
+
       const response = await api
         .get("/admin/variants?q=Test product1", {
           headers: {
@@ -145,4 +149,119 @@ describe("/admin/products", () => {
       )
     })
   })
+
+  describe("GET /admin/variants price selection strategy", () => {
+    beforeEach(async () => {
+      try {
+        await adminVariantsSeeder(dbConnection)
+      } catch (err) {
+        console.log(err)
+      }
+      await adminSeeder(dbConnection)
+    })
+
+    afterEach(async () => {
+      const db = useDb()
+      await db.teardown()
+    })
+
+    it("selects prices based on the passed currency code", async () => {
+      const api = useApi()
+
+      const response = await api.get(
+        "/admin/variants?id=test-variant&currency_code=usd",
+        {
+          headers: {
+            Authorization: "Bearer test_token",
+          },
+        }
+      )
+
+      expect(response.data).toMatchSnapshot({
+        variants: [
+          {
+            id: "test-variant",
+            original_price: 100,
+            calculated_price: 80,
+            calculated_price_type: "sale",
+            original_price_incl_tax: null,
+            calculated_price_incl_tax: null,
+            original_tax: null,
+            calculated_tax: null,
+            options: expect.any(Array),
+            prices: expect.any(Array),
+            product: expect.any(Object),
+            created_at: expect.any(String),
+            updated_at: expect.any(String),
+          },
+        ],
+      })
+    })
+
+    it("selects prices based on the passed region id", async () => {
+      const api = useApi()
+
+      const response = await api.get(
+        "/admin/variants?id=test-variant&region_id=reg-europe",
+        {
+          headers: {
+            Authorization: "Bearer test_token",
+          },
+        }
+      )
+
+      expect(response.data).toMatchSnapshot({
+        variants: [
+          {
+            id: "test-variant",
+            original_price: 100,
+            calculated_price: 80,
+            calculated_price_type: "sale",
+            original_price_incl_tax: 100,
+            calculated_price_incl_tax: 80,
+            original_tax: 0,
+            calculated_tax: 0,
+            options: expect.any(Array),
+            prices: expect.any(Array),
+            product: expect.any(Object),
+            created_at: expect.any(String),
+            updated_at: expect.any(String),
+          },
+        ],
+      })
+    })
+
+    it("selects prices based on the passed region id and customer id", async () => {
+      const api = useApi()
+
+      const response = await api.get(
+        "/admin/variants?id=test-variant&region_id=reg-europe&customer_id=test-customer",
+        {
+          headers: {
+            Authorization: "Bearer test_token",
+          },
+        }
+      )
+
+      expect(response.data).toMatchSnapshot({
+        variants: [
+          {
+            id: "test-variant",
+            original_price: 100,
+            calculated_price: 40,
+            calculated_price_type: "sale",
+            original_price_incl_tax: 100,
+            calculated_price_incl_tax: 40,
+            original_tax: 0,
+            calculated_tax: 0,
+            prices: expect.any(Array),
+            options: expect.any(Array),
+            product: expect.any(Object),
+            created_at: expect.any(String),
+            updated_at: expect.any(String),
+          },
+        ],
+      })
+    })
+  })
 })