test: unit tests for the SEO classes

Pure tests of the classes package (no database): the resolver's value
chains with every layer present and absent, robots per directive, the
staging lock and drafts; the redirect graph (chains, flattened and
back-and-forth graphs, loops by exact, pattern and regex probes, the
10-hop cap); URL normalisation across every address rule; the robots
grammar over every directive combination; Google's robots.txt matcher
examples; templates and unknown placeholders; CSV export and import;
owner resolution; and every kind of the issue report.

go.mod: gorm.io/driver/postgres becomes a direct requirement (the tests'
dry-run database).

classes/templates_test.go

@@ -0,0 +1,75 @@
+package classes
+
+import (
+	"testing"
+
+	"git.golem15.com/golem15/sm-seo-plugin/models"
+)
+
+// TestTemplates: rendering fills the three placeholders, collapses spaces
+// and trims separators an empty placeholder leaves; an unknown placeholder
+// is refused when the template is saved.
+func TestTemplates(t *testing.T) {
+	vars := TemplateVars{Title: "Grzyby leśne", Description: "O grzybach", Site: "Atlas"}
+	for _, tc := range []struct {
+		name, tpl string
+		vars      TemplateVars
+		want      string
+	}{
+		{"title and site", "%title% | %site%", vars, "Grzyby leśne | Atlas"},
+		{"description", "%description% – %site%", vars, "O grzybach – Atlas"},
+		{"every placeholder twice", "%title% %title% %site%", vars, "Grzyby leśne Grzyby leśne Atlas"},
+		{"an empty site leaves no separator", "%title% | %site%", TemplateVars{Title: "About"}, "About"},
+		{"an empty title leaves no separator", "%title% · %site%", TemplateVars{Site: "Atlas"}, "Atlas"},
+		{"separators of every kind are trimmed", "%title% — : , %site%", TemplateVars{Title: "X"}, "X"},
+		{"inner separators stay", "%title% | Blog | %site%", TemplateVars{Title: "X", Site: "Y"}, "X | Blog | Y"},
+		{"runs of spaces collapse", "  %title%   \t  %site%  ", vars, "Grzyby leśne Atlas"},
+		{"an empty template renders nothing", "", vars, ""},
+		{"a blank template renders nothing", "   ", vars, ""},
+		{"text without placeholders", "Static title", vars, "Static title"},
+		{"an unknown placeholder renders as written", "%title% %author%", vars, "Grzyby leśne %author%"},
+		{"everything empty", "%title% | %site%", TemplateVars{}, ""},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := RenderTemplate(tc.tpl, tc.vars); got != tc.want {
+				t.Fatalf("RenderTemplate(%q) = %q, want %q", tc.tpl, got, tc.want)
+			}
+		})
+	}
+
+	for _, tc := range []struct {
+		tpl, unknown string
+	}{
+		{"%title% | %site%", ""},
+		{"%description%", ""},
+		{"", ""},
+		{"100% sure", ""},
+		{"%author% | %site%", "%author%"},
+		{"%title% %Title%", "%Title%"},
+		{"%%", "%%"},
+		{"%site_name%", "%site_name%"},
+		{"%title% %date% %page%", "%date%"},
+	} {
+		if got := models.UnknownPlaceholder(tc.tpl); got != tc.unknown {
+			t.Errorf("UnknownPlaceholder(%q) = %q, want %q", tc.tpl, got, tc.unknown)
+		}
+		problems := models.TemplateProblems(tc.tpl)
+		if tc.unknown == "" && problems != nil {
+			t.Errorf("TemplateProblems(%q) = %+v", tc.tpl, problems)
+		}
+		if tc.unknown != "" && (len(problems) != 1 || problems[0].Key != "golem15.seo::lang.settings.template_unknown" || problems[0].Params["placeholder"] != tc.unknown) {
+			t.Errorf("TemplateProblems(%q) = %+v", tc.tpl, problems)
+		}
+	}
+
+	refused := models.Settings{TitleTemplate: "%title% | %brand%", HomeTemplate: "%site% %x%"}.Problems()
+	if len(refused["title_template"]) != 1 || len(refused["home_template"]) != 1 {
+		t.Fatalf("settings problems = %+v", refused)
+	}
+	if ok := (models.Settings{TitleTemplate: "%title% | %site%", HomeTemplate: "%site%"}).Problems(); len(ok) != 0 {
+		t.Fatalf("valid templates refused: %+v", ok)
+	}
+	if len(models.KnownPlaceholders) != 3 || PlaceholderTitle != models.KnownPlaceholders[0] || PlaceholderDescription != models.KnownPlaceholders[1] || PlaceholderSite != models.KnownPlaceholders[2] {
+		t.Fatalf("the rendered and the validated placeholders differ: %v", models.KnownPlaceholders)
+	}
+}