Use shared envTest for unit tests

Speed up unit tests by using a shared envTest. This requires each
test to use its own namespace to avoid clobbering objects for
other tests. Tests previously took around 8 seconds each, and now
the initial test takes 2 seconds with follow up tests taking less
than a second each.

Also update existing tests that use a fixed namespace to use a
generated namespace.

Share gold file template function with yaml files.

Remove the testClusterMode, and instead rely on MainTest to do
the appropriate test setup and rootArgs flag setup. Move the
rootArg flag setup out of NewTestEnvKubeManager to avoid
side effects.

A follow up change can be to push the individual setups
from NewTestEnvKubeManager() into their respective TestMain since
the harness share little code.

Signed-off-by: Allen Porter <allen@thebends.org>

cmd/flux/main_unit_test.go

@@ -3,12 +3,32 @@
 package main
 
 import (
+	"fmt"
 	"os"
 	"testing"
 )
 
+// The test environment is long running process shared between tests, initialized
+// by a `TestMain` function depending on how the test is involved and which tests
+// are a part of the build.
+var testEnv *testEnvKubeManager
+
 func TestMain(m *testing.M) {
 	// Ensure tests print consistent timestamps regardless of timezone
 	os.Setenv("TZ", "UTC")
-	os.Exit(m.Run())
+
+	// Creating the test env manager sets rootArgs client flags
+	km, err := NewTestEnvKubeManager(TestEnvClusterMode)
+	if err != nil {
+		panic(fmt.Errorf("error creating kube manager: '%w'", err))
+	}
+	testEnv = km
+	rootArgs.kubeconfig = testEnv.kubeConfigPath
+
+	// Run tests
+	code := m.Run()
+
+	km.Stop()
+
+	os.Exit(code)
 }