backend_fiesta/models/nutrition_test.go

package models

import "testing"

/*
Reading the catalogue's nutrition strings.

The catalogue holds nutrition as display lines — "Energy 350kcal" — and the app
needs figures. These are the shapes those lines actually come in, and the ones
they come in when a scrape goes sideways.

The rule throughout: never invent a number, and never lose label text. A line
that cannot be read is carried whole rather than dropped, because it is
something a manufacturer printed on a packet and this code is not the authority
on what belongs on a food label.
*/

func TestAPlainLineBecomesAFigure(t *testing.T) {
	panel := NutritionFromLines([]string{"Energy 350kcal"})
	if !panel.HasValues() {
		t.Fatal("nothing parsed")
	}
	got := panel.Items[0]
	if got.Name != "Energy" || got.Value != 350 || got.Unit != "kcal" {
		t.Fatalf("got %+v", got)
	}
}

func TestTheSeparatorsThatActuallyOccur(t *testing.T) {
	// Colons, multi-word names and a space before the unit are all in the wild,
	// and each one used to be a whole line lost.
	for _, tc := range []struct {
		line  string
		name  string
		value float64
		unit  string
	}{
		{"Protein: 6.5 g", "Protein", 6.5, "g"},
		{"Total Sugars 22g", "Total Sugars", 22, "g"},
		{"Saturated Fat 11.5 g", "Saturated Fat", 11.5, "g"},
		{"Sodium 310mg", "Sodium", 310, "mg"},
		{"Energy - 520 kcal", "Energy", 520, "kcal"},
	} {
		panel := NutritionFromLines([]string{tc.line})
		if !panel.HasValues() {
			t.Errorf("%q parsed to nothing", tc.line)
			continue
		}
		got := panel.Items[0]
		if got.Name != tc.name || got.Value != tc.value || got.Unit != tc.unit {
			t.Errorf("%q → %+v, want {%s %v %s}", tc.line, got, tc.name, tc.value, tc.unit)
		}
	}
}

func TestADecimalSurvives(t *testing.T) {
	// Saturated fat is 11.5g as often as 11g. Rounding to please a type would be
	// editing a food label.
	panel := NutritionFromLines([]string{"Saturated Fat 11.5g"})
	if panel.Items[0].Value != 11.5 {
		t.Fatalf("got %v, want 11.5", panel.Items[0].Value)
	}
}

func TestALineWithNoNumberIsKeptWhole(t *testing.T) {
	// Real label text. Dropping it loses something a manufacturer printed;
	// forcing a 0 into it states something false about the food.
	panel := NutritionFromLines([]string{"Contains permitted natural colour"})
	if !panel.HasValues() {
		t.Fatal("the line was dropped")
	}
	got := panel.Items[0]
	if got.Name != "Contains permitted natural colour" {
		t.Fatalf("the text was mangled: %+v", got)
	}
	if got.Value != 0 || got.Unit != "" {
		t.Fatalf("a figure was invented for a line that had none: %+v", got)
	}
}

func TestAUnitlessFigureKeepsItsNumber(t *testing.T) {
	// "Servings per pack 4" has a real number and no unit.
	panel := NutritionFromLines([]string{"Servings per pack 4"})
	got := panel.Items[0]
	if got.Name != "Servings per pack" || got.Value != 4 || got.Unit != "" {
		t.Fatalf("got %+v", got)
	}
}

func TestPercentAndMicrogramsAreUnits(t *testing.T) {
	for _, tc := range []struct{ line, unit string }{
		{"Vitamin C 45%", "%"},
		{"Vitamin B12 1.2µg", "µg"},
	} {
		panel := NutritionFromLines([]string{tc.line})
		if !panel.HasValues() || panel.Items[0].Unit != tc.unit {
			t.Errorf("%q → %+v, want unit %q", tc.line, panel.Items[0], tc.unit)
		}
	}
}

func TestBlanksAndBareNumbersAreNotRows(t *testing.T) {
	// A blank is nothing. A bare "100" has no label, and an unnamed row on a
	// nutrition panel is noise a shopper cannot use.
	if panel := NutritionFromLines([]string{"", "   ", "100"}); panel != nil {
		t.Fatalf("made a panel out of nothing: %+v", panel)
	}
}

func TestNoLinesMeansNoPanel(t *testing.T) {
	// nil rather than an empty panel, so a caller can tell "no nutrition known"
	// from "a panel that happens to be empty" — the endpoint omits the first.
	if NutritionFromLines(nil) != nil {
		t.Fatal("an absent panel was reported as present")
	}
	if NutritionFromLines([]string{}) != nil {
		t.Fatal("an absent panel was reported as present")
	}
}

func TestAnEmptyPanelIsNotWorthSending(t *testing.T) {
	// `items: []` on a product page renders as an empty box, which reads as
	// "this food has no nutrition" rather than "we do not know yet".
	var absent *NutritionPanel
	if absent.HasValues() {
		t.Fatal("nil reported as having values")
	}
	if (&NutritionPanel{Per: "100g"}).HasValues() {
		t.Fatal("a panel with a basis and no rows reported as having values")
	}
}

func TestTheDerivedPanelDoesNotGuessItsBasis(t *testing.T) {
	// The strings never carried one. "100g" is the common case and not the only
	// one, and a wrong basis makes every figure beneath it a misstatement rather
	// than an unknown.
	panel := NutritionFromLines([]string{"Energy 350kcal"})
	if panel.Per != "" || panel.Servingsize != "" {
		t.Fatalf("invented a basis: per=%q servingsize=%q", panel.Per, panel.Servingsize)
	}
}