template: add tests, fix up easy holes

should cope with double-braced blocks now (treating them the same as
single-braced. templateEmail now returns an error, which should not be
seen as catastrophic, but reports likely mistakes.

template_test.go

@@ -0,0 +1,128 @@
+package main
+
+import (
+	"strings"
+	"testing"
+)
+
+// In == Out when nothing is meant to be templated.
+func TestBlankTemplate(t *testing.T) {
+	in := `Success, user! Your account has been created. Log in at myAccountURL with your username to get started.`
+
+	out, err := templateEmail(in, []string{}, []string{}, map[string]any{})
+
+	if err != nil {
+		t.Fatalf("error: %+v", err)
+	}
+
+	if out != in {
+		t.Fatalf(`returned string doesn't match input: "%+v" != "%+v"`, out, in)
+	}
+}
+
+func testConditional(isTrue bool, t *testing.T) {
+	in := `Success, {username}! Your account has been created. {if myCondition}Log in at {myAccountURL} with username {username} to get started.{endif}`
+
+	vars := []string{"{username}", "{myAccountURL}", "{myCondition}"}
+	conds := vars
+	vals := map[string]any{
+		"username":     "TemplateUsername",
+		"myAccountURL": "TemplateURL",
+		"myCondition":  isTrue,
+	}
+
+	out, err := templateEmail(in, vars, conds, vals)
+
+	target := ""
+	if isTrue {
+		target = `Success, {username}! Your account has been created. Log in at {myAccountURL} with username {username} to get started.`
+	} else {
+		target = `Success, {username}! Your account has been created. `
+	}
+
+	target = strings.ReplaceAll(target, "{username}", vals["username"].(string))
+	target = strings.ReplaceAll(target, "{myAccountURL}", vals["myAccountURL"].(string))
+
+	if err != nil {
+		t.Fatalf("error: %+v", err)
+	}
+
+	if out != target {
+		t.Fatalf(`returned string doesn't match desired output: "%+v" != "%+v"`, out, target)
+	}
+}
+
+func TestConditionalTrue(t *testing.T) {
+	testConditional(true, t)
+}
+
+func TestConditionalFalse(t *testing.T) {
+	testConditional(false, t)
+}
+
+// Template mistakenly double-braced values, but return a warning.
+func TestTemplateDoubleBraceGracefulHandling(t *testing.T) {
+	in := `Success, {{username}}! Your account has been created. Log in at {myAccountURL} with username {username} to get started.`
+
+	vars := []string{"{username}", "{myAccountURL}"}
+	vals := map[string]any{
+		"username":     "TemplateUsername",
+		"myAccountURL": "TemplateURL",
+	}
+
+	target := strings.ReplaceAll(in, "{{username}}", vals["username"].(string))
+	target = strings.ReplaceAll(target, "{username}", vals["username"].(string))
+	target = strings.ReplaceAll(target, "{myAccountURL}", vals["myAccountURL"].(string))
+
+	out, err := templateEmail(in, vars, []string{}, vals)
+
+	if err == nil {
+		t.Fatal("no error when given double-braced variable")
+	}
+
+	if out != target {
+		t.Fatalf(`returned string doesn't match desired output: "%+v" != "%+v"`, out, target)
+	}
+}
+
+func TestVarAtAnyPosition(t *testing.T) {
+	in := `Success, user! Your account has been created. Log in at myAccountURL with your username to get started.`
+	vars := []string{"{username}", "{myAccountURL}"}
+	vals := map[string]any{
+		"username":     "TemplateUsername",
+		"myAccountURL": "TemplateURL",
+	}
+
+	for i := range in {
+		newIn := in[0:i] + vars[0] + in[i:]
+
+		target := strings.ReplaceAll(newIn, vars[0], vals["username"].(string))
+
+		out, err := templateEmail(newIn, vars, []string{}, vals)
+
+		if err != nil {
+			t.Fatalf("error: %+v", err)
+		}
+
+		if out != target {
+			t.Fatalf(`returned string doesn't match desired output: "%+v" != "%+v"`, out, target)
+		}
+	}
+}
+
+func TestIncompleteBlock(t *testing.T) {
+	in := `Success, user! Your account has been created. Log in at myAccountURL with your username to get started.`
+	for i := range in {
+		newIn := in[0:i] + "{" + in[i:]
+
+		out, err := templateEmail(newIn, []string{"a"}, []string{"a"}, map[string]any{"a": "a"})
+
+		if out != newIn {
+			t.Fatalf(`returned string for position %d/%d doesn't match desired output: "%+v" != "%+v"`, i+1, len(newIn), out, newIn)
+		}
+		if err == nil {
+			t.Fatalf("no error when given incomplete block with brace at position %d/%d", i+1, len(newIn))
+		}
+
+	}
+}