refactor(inputloader): all fast tests together (#269)

This change allows us to have all fasts tests together. They are
mostly unit tests or integration tests that do not require the
network. The advantage of this strategy is the following. We can
now run all these tests with a single click in VSCode. In turn,
doing that tells us which lines of code we are not covering.

The tests requiring the network are in a separate file, so we can
easily see which lines of code are testing without using the network
and which ones instead depend on that. (Currently, 100% of the
inputloader.go file is tested without using the network.)

While there, rename the other file such that is clear that it
contains tests requiring the network. We now have some tests in
inputloader_test.go that are not strictly unit tests.

This refactoring was identified as useful while working
on https://github.com/ooni/probe/issues/1299.

internal/engine/inputloader_network_test.go

@@ -0,0 +1,46 @@
+package engine_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/apex/log"
+	engine "github.com/ooni/probe-cli/v3/internal/engine"
+	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/engine/model"
+)
+
+func TestInputLoaderInputOrQueryBackendWithNoInput(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skip test in short mode")
+	}
+	sess, err := engine.NewSession(engine.SessionConfig{
+		AvailableProbeServices: []model.Service{{
+			Address: "https://ams-pg-test.ooni.org/",
+			Type:    "https",
+		}},
+		AssetsDir:       "testdata",
+		KVStore:         kvstore.NewMemoryKeyValueStore(),
+		Logger:          log.Log,
+		SoftwareName:    "miniooni",
+		SoftwareVersion: "0.1.0-dev",
+		TempDir:         "testdata",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer sess.Close()
+	il := engine.NewInputLoader(engine.InputLoaderConfig{
+		InputPolicy: engine.InputOrQueryBackend,
+		Session:     sess,
+	})
+	ctx := context.Background()
+	out, err := il.Load(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(out) < 10 {
+		// check-in SHOULD return AT LEAST 20 URLs at a time.
+		t.Fatal("not the output length we expected")
+	}
+}