helper/resource: Add (testing.T).Logf() call and augment documentation for TestStep.SkipFunc (#889)

Reference: #824
Reference: https://pkg.go.dev/testing#T.Logf

The additional logging will be more visible, as it will appear in stdout instead of disabled by default.

The documentation updates should make the purpose and correct usage of this field more clear.

Author: bflad

.changelog/889.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+helper/resource: Added more visible logging for test steps skipped via the `TestStep` type `SkipFunc` field.
+```

helper/resource/testing.go

@@ -452,8 +452,15 @@ type TestStep struct {
 	// are tested alongside real resources
 	PreventPostDestroyRefresh bool
 
-	// SkipFunc is called before applying config, but after PreConfig
-	// This is useful for defining test steps with platform-dependent checks
+	// SkipFunc enables skipping the TestStep, based on environment criteria.
+	// For example, this can prevent running certain steps that may be runtime
+	// platform or API configuration dependent.
+	//
+	// Return true with no error to skip the test step. The error return
+	// should be used to signify issues that prevented the function from
+	// completing as expected.
+	//
+	// SkipFunc is called after PreConfig but before applying the Config.
 	SkipFunc func() (bool, error)
 
 	//---------------------------------------------------------------

helper/resource/testing_new.go

@@ -109,7 +109,8 @@ func runNewTest(t testing.T, c TestCase, helper *plugintest.Helper) {
 				t.Fatal(err)
 			}
 			if skip {
-				log.Printf("[WARN] Skipping step %d/%d", i+1, len(c.Steps))
+				t.Logf("Skipping step %d/%d due to SkipFunc", i+1, len(c.Steps))
+				log.Printf("[WARN] Skipping step %d/%d due to SkipFunc", i+1, len(c.Steps))
 				continue
 			}
 		}