api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/smtp_configure_test.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func cleanSmtpVars() {
+	for _, env := range []string{"SMTP_USERNAME", "SMTP_PASSWORD", "SMTP_HOST", "SMTP_FROM_ADDRESS"} {
+		os.Setenv(env, "")
+	}
+}
+
+func TestSmtpConfigureBasics(t *testing.T) {
+	failTestOnError(t, setupTestEnv())
+
+	os.Setenv("SMTP_USERNAME", "test@example.com")
+	os.Setenv("SMTP_PASSWORD", "hunter2")
+	os.Setenv("SMTP_HOST", "smtp.commento.io")
+	os.Setenv("SMTP_FROM_ADDRESS", "no-reply@commento.io")
+
+	if err := smtpConfigure(); err != nil {
+		t.Errorf("unexpected error when configuring SMTP: %v", err)
+		return
+	}
+
+	cleanSmtpVars()
+}
+
+func TestSmtpConfigureEmptyHost(t *testing.T) {
+	failTestOnError(t, setupTestEnv())
+
+	os.Setenv("SMTP_USERNAME", "test@example.com")
+	os.Setenv("SMTP_PASSWORD", "hunter2")
+	os.Setenv("SMTP_FROM_ADDRESS", "no-reply@commento.io")
+
+	if err := smtpConfigure(); err != nil {
+		t.Errorf("unexpected error when configuring SMTP: %v", err)
+		return
+	}
+
+	if smtpConfigured {
+		t.Errorf("SMTP configured when it should not be due to empty SMTP_HOST")
+		return
+	}
+
+	cleanSmtpVars()
+}
+
+func TestSmtpConfigureEmptyAddress(t *testing.T) {
+	failTestOnError(t, setupTestEnv())
+
+	os.Setenv("SMTP_USERNAME", "test@example.com")
+	os.Setenv("SMTP_PASSWORD", "hunter2")
+	os.Setenv("SMTP_HOST", "smtp.commento.io")
+
+	if err := smtpConfigure(); err == nil {
+		t.Errorf("expected error not found; SMTP should not be configured when SMTP_FROM_ADDRESS is empty")
+		return
+	}
+
+	cleanSmtpVars()
+}