Proposal: Properly use contexts in functional tests

Signed-off-by: Nahshon Unna-Tsameret <[email protected]>

design-proposals/testing-and-ci/properly-using-context-in-functional-tests.md

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+# Properly use contexts in functional tests
+
+## Overview
+This proposal is about properly use golang contexts in KubeVirt functional tests.
+
+## Introduction
+Since the start of the KubeVirt project, contexts became a very important concept
+in golang, when writing an asynchronous logic. In a way, the KubeVirt code left
+behind regarding the proper usage of golang contexts.
+
+Using `context.Background()` or even worse, `context.TODO()` is a code smell, because
+doing that won't allow the application to cancel async-operation, like I/O, for example,
+in case of termination.
+
+Closing this gap is a huge effort. Contexts should be passed deeper and deeper down
+the call stack, changing the api of many functions and methods. The impact is meaningful.
+
+The situation in the functional test is a much easier to handle. ginkgo documentation
+describes how to deal with interrupts, by letting ginkgo inject context object to
+the tests. See here for more details:
+[https://onsi.github.io/ginkgo/#spec-timeouts-and-interruptible-nodes](https://onsi.github.io/ginkgo/#spec-timeouts-and-interruptible-nodes)
+
+## Goals
+- Define coding standards for the functional tests, regarding the proper way of using contexts
+- Modify the current code to use the new standards
+- Using the new standards as a gate for code review of functional tests
+
+## Design 
+### Coding Standards for Using contexts in Functional Tests
+
+To make sure that any asynchronous operation is canceled when a test is
+terminated, make sure to use golang contexts properly. See more details in
+[ginkgo documentation](https://onsi.github.io/ginkgo/#spec-timeouts-and-interruptible-nodes)
+
+Avoid using new contexts (e.g. `context.Background()` or `context.TODO()`).
+Instead, prefer using the context injected by ginkgo.
+
+First, add the `ctx` optional parameter of the anonymous functions in `It`, `BeforeEach`,
+`AfterEach` or `DescribeTable`. Then use this parameter for all places where a context is 
+needed in this container.
+
+ginkgo will inject a context to the test, by populating the `ctx` parameter with a context 
+controlled by ginkgo.
+
+For example:
+```go
+It("should test something", func(ctx context.Context){
+	...
+	kv, err = virtClient.KubeVirt(kvName).Update(ctx, kv, metav1.UpdateOptions{})
+	Expect(err).ToNot(HaveOccurred())
+	...
+})
+```
+
+When using asynchronous assertion, i.e. `Eventually` or `Consistently`, pass the container's context
+using the `WithContext` method, and add the context parameter to the checked function; e.g.
+```go
+It("should test something", func(ctx context.Context){
+	...
+
+	Eventually(func(ctx context.Context) error {
+		kv, err = virtClient.KubeVirt(kvName).Update(ctx, kv, metav1.UpdateOptions{})
+		...
+
+		return err
+	}).WithTimeout(120 * time.Seconds).
+		WithPolling(10 * time.Seconds).
+		WithContext(ctx).
+		Should(Succeed())
+
+	...
+})
+```
+
+Notice that in case of also passing the `Gomega` parameter, the context parameter will be the second one, i.e.
+```go
+It("should test something", func (ctx context.Context){
+	...
+
+	Eventually(func(g Gomega, ctx context.Context) {
+		kv, err = virtClient.KubeVirt(kvName).Update(ctx, kv, metav1.UpdateOptions{})
+		g.Expect(err).ToNot(HaveOccurred())
+		...
+	}).WithTimeout(120 * time.Seconds).
+		WithPolling(10 * time.Seconds).
+		WithContext(ctx).
+		Should(Succeed())
+
+	...
+})
+```
+
+Also, notice that gingko cancels contexts when exiting a container, therefore avoid using the same context across 
+multiple containers. This example will fail with canceled context error:
+```go
+var _ = Describe("test something", func(){
+	var ctx context.Context
+
+	BeforeEach(func(gctx context.Context){
+		ctx = gctx // or something like ctx = context.WithTimeout(gctx, ...)
+	})
+
+	It(func(){
+		kv, err = virtClient.KubeVirt(kvName).Update(ctx, kv, metav1.UpdateOptions{}) // <= will fail here
+		...
+	})
+})
+```
+
+#### Bad Example
+```go
+It("should test something", func(){
+	...
+	kv, err = virtClient.KubeVirt(kvName).Update(context.Backgound(), kv, metav1.UpdateOptions{})
+	Expect(err).ToNot(HaveOccurred())
+	...
+})
+```
+The above example, uses a new context when performing an I/O operation - using the client to perform
+a call to the kubernets cluster. This context can't be canceled and in case of interrupt, this is not 
+handled properly. Using the ginkgo context, will cause a proper cancellation of the I/O operation in
+this case.
+
+## Additional Reading
+* [ginkgo documentation](https://onsi.github.io/ginkgo/#spec-timeouts-and-interruptible-nodes)
+* [kubernetes coding standards](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-testing/writing-good-e2e-tests.md#interrupting-tests)
+
+## Related PRs
+* HCO implementation: [hyperconverged-cluster-operator/pull/2952](https://github.com/kubevirt/hyperconverged-cluster-operator/pull/2952)
+* First KubeVirt PR to start implementing the new coding standards: [kubevirt/pull/12140](https://github.com/kubevirt/kubevirt/pull/12140)
+  (Halt. Waiting for this proposal)
+* KubeVirt coding standards: [kubevirt/pull/12148](https://github.com/kubevirt/kubevirt/pull/12148)
+  (Reverted. Waiting for this proposal)