test: unit tests for heading conversion, image alt, content facts and related settings

- ConvertContentH1 and ConvertTranslationH1 for post bodies and category
  pillar text
- SetImageAlt with several matches, repeated alt attributes and markup
  that only looks like an img
- the content facts outline, images, decorative images and embeds
- the related-posts mode and count

classes/image_alt_test.go

@@ -20,3 +20,28 @@ func TestSetImageAlt(t *testing.T) {
 		t.Fatalf("missing = %q, %d", out, n)
 	}
 }
+
+// TestSetImageAltEdges pins the edges: every matching img is rewritten
+// and counted (the first one's old alt answered), repeated alt attributes
+// collapse to one, a src given escaped does not match the unescaped one,
+// an empty src and a body without img change nothing, and text that
+// looks like an img inside a comment or script is not touched.
+func TestSetImageAltEdges(t *testing.T) {
+	doc := `<img src="a.jpg" alt="one"><p>t</p><img alt="x" src="a.jpg" alt="y"><!-- <img src="a.jpg"> --><script>"<img src=a.jpg>"</script>`
+	out, n, old := SetImageAlt(doc, "a.jpg", "new")
+	if n != 2 || old == nil || *old != "one" {
+		t.Fatalf("n=%d old=%v", n, old)
+	}
+	want := `<img src="a.jpg" alt="new"><p>t</p><img alt="new" src="a.jpg"><!-- <img src="a.jpg"> --><script>"<img src=a.jpg>"</script>`
+	if out != want {
+		t.Fatalf("out = %q\nwant  %q", out, want)
+	}
+	if out, n, _ := SetImageAlt(`<img src="a.jpg?x=1&amp;y=2">`, "a.jpg?x=1&amp;y=2", "z"); n != 0 || out != `<img src="a.jpg?x=1&amp;y=2">` {
+		t.Fatalf("escaped src matched: %q %d", out, n)
+	}
+	for _, tc := range []struct{ html, src string }{{`<img src="a.jpg">`, ""}, {`<p>no images</p>`, "a.jpg"}, {"", "a.jpg"}} {
+		if out, n, old := SetImageAlt(tc.html, tc.src, "x"); out != tc.html || n != 0 || old != nil {
+			t.Errorf("SetImageAlt(%q, %q) = %q %d %v", tc.html, tc.src, out, n, old)
+		}
+	}
+}