Fix TestEnvWithDefault and TestContainerCMDEventToStderr (elastic#5361)

Now TestEnvWithDefault unsets all environment variables it sets,
allowing it to be run multiple times using `-count`.

TestContainerCMDEventToStderr did not call agentFixture.Prepare early
enough leading to an empty STATE_PATH env var, so all state
information was in /usr/share/elastic-agent, which could make
subsequent tests to fail because they could read
/usr/share/elastic-agent/state/container-paths.yml and use a state
path different than the one set in the test.

---------

Co-authored-by: Paolo Chilà <[email protected]>

internal/pkg/agent/cmd/container_test.go

@@ -24,11 +24,13 @@ func TestEnvWithDefault(t *testing.T) {
 	require.Equal(t, def, res)
 
 	err := os.Setenv(key1, "key1")
+	defer os.Unsetenv(key1)
 	if err != nil {
 		t.Skipf("could not export env var: %s", err)
 	}
 
 	err = os.Setenv(key2, "key2")
+	defer os.Unsetenv(key2)
 	if err != nil {
 		t.Skipf("could not export env var: %s", err)
 	}

testing/integration/container_cmd_test.go

@@ -327,6 +327,9 @@ func TestContainerCMDEventToStderr(t *testing.T) {
 	agentFixture, err := define.NewFixtureFromLocalBuild(t, define.Version())
 	require.NoError(t, err)
 
+	// We call agentFixture.Prepare to set the workdir
+	require.NoError(t, agentFixture.Prepare(ctx), "failed preparing agent fixture")
+
 	_, outputID := createMockESOutput(t, info)
 	policyID, enrollmentAPIKey := createPolicy(
 		t,
@@ -366,7 +369,7 @@ func TestContainerCMDEventToStderr(t *testing.T) {
 		// the agent logs will be present in the error message
 		// which should help to explain why the agent was not
 		// healthy.
-		err := agentFixture.IsHealthy(ctx)
+		err := agentFixture.IsHealthy(ctx, withEnv(env))
 		return err == nil
 	},
 		2*time.Minute, time.Second,