Implement two-phase project loading

__test__/projects/CachingProjectListDataSource.test.ts

@@ -0,0 +1,102 @@
+import { ProjectSummary, CachingProjectListDataSource } from "@/features/projects/domain"
+
+const projects: ProjectSummary[] = [{
+  id: "acme-foo",
+  name: "foo",
+  displayName: "Foo",
+  owner: "acme",
+  ownerUrl: "https://github.com/acme"
+}]
+
+test("It returns cached projects when cache is populated", async () => {
+  let didCallDataSource = false
+  const sut = new CachingProjectListDataSource({
+    dataSource: {
+      async getProjectList() {
+        didCallDataSource = true
+        return projects
+      }
+    },
+    repository: {
+      async get() {
+        return projects
+      },
+      async set() {},
+      async delete() {}
+    }
+  })
+  const result = await sut.getProjectList()
+  expect(result).toEqual(projects)
+  expect(didCallDataSource).toBe(false)
+})
+
+test("It fetches and caches projects when cache is empty", async () => {
+  let cachedProjects: ProjectSummary[] | undefined
+  const sut = new CachingProjectListDataSource({
+    dataSource: {
+      async getProjectList() {
+        return projects
+      }
+    },
+    repository: {
+      async get() {
+        return undefined
+      },
+      async set(value) {
+        cachedProjects = value
+      },
+      async delete() {}
+    }
+  })
+  const result = await sut.getProjectList()
+  expect(result).toEqual(projects)
+  expect(cachedProjects).toEqual(projects)
+})
+
+test("It treats an empty cached list as a valid cache hit and does not call the data source", async () => {
+  let didCallDataSource = false
+  const sut = new CachingProjectListDataSource({
+    dataSource: {
+      async getProjectList() {
+        didCallDataSource = true
+        return []
+      }
+    },
+    repository: {
+      async get() {
+        return []
+      },
+      async set() {},
+      async delete() {}
+    }
+  })
+  const result = await sut.getProjectList()
+  expect(result).toEqual([])
+  expect(didCallDataSource).toBe(false)
+})
+
+test("It bypasses cache and refreshes when refresh=true", async () => {
+  let didCallDataSource = false
+  let cachedProjects: ProjectSummary[] | undefined
+  const sut = new CachingProjectListDataSource({
+    dataSource: {
+      async getProjectList() {
+        didCallDataSource = true
+        return projects
+      }
+    },
+    repository: {
+      async get() {
+        return projects
+      },
+      async set(value) {
+        cachedProjects = value
+      },
+      async delete() {}
+    }
+  })
+  const result = await sut.getProjectList({ refresh: true })
+  expect(result).toEqual(projects)
+  expect(didCallDataSource).toBe(true)
+  expect(cachedProjects).toEqual(projects)
+})