Golden test pinning the seeded output of each part of the token grammar

template_stability_test.go

@@ -0,0 +1,41 @@
+package fakes
+
+import "testing"
+
+// TestSeededOutputIsStable pins the exact bytes a seeded faker emits for each
+// piece of the token grammar, so a change to how a format is scanned or rendered
+// cannot quietly shift the rng stream that reproducibility depends on.
+func TestSeededOutputIsStable(t *testing.T) {
+	dir := writeData(t, map[string]string{
+		"alt":     `{"format":"{a|b}","a":["A"],"b":["B"]}`,
+		"calc":    `{"format":"{net} x {qty} = {calc(net * qty, 2)}","net":["19.99"],"qty":["3"]}`,
+		"classes": `{"format":"00-11-AA-aa"}`,
+		"escapes": `{"format":"#0#1#A#a##{x}","x":["!"]}`,
+		"funcs":   `{"format":"{hex(6)} {int(10,99)} {float(0,1,3)} {nanoid(5)} {seq()}"}`,
+		"nested":  `{"format":"{outer}","outer":[{"format":"{inner}-00","inner":["i"]}]}`,
+		"ref":     `{"format":"see {..alt}"}`,
+		"repeat":  `{"format":"{w}","repeat":4,"separator":",","w":["x","y","z"]}`,
+		"sums":    `{"format":"9{d}{luhn()} {e}{ean()} {m}{mod11()}","d":["012345678901234"],"e":["123456789012"],"m":["12345678"]}`,
+		"weights": `[{"format":"big","weight":9},{"format":"tiny","weight":1}]`,
+	})
+	want := map[string][]string{
+		"alt":     {"A", "B", "A", "A"},
+		"calc":    {"19.99 x 3 = 59.97", "19.99 x 3 = 59.97", "19.99 x 3 = 59.97", "19.99 x 3 = 59.97"},
+		"classes": {"49-74-VY-gj", "38-68-RP-xo", "47-68-IB-hs", "91-89-LP-gk"},
+		"escapes": {"01Aa#!", "01Aa#!", "01Aa#!", "01Aa#!"},
+		"funcs":   {"0016a2 33 0.649 k4Kwj 1", "a00c07 84 0.175 6UjGv 2", "f70eb8 12 0.390 p5p6g 3", "9048a3 90 0.531 I3Aqv 4"},
+		"nested":  {"i-89", "i-67", "i-47", "i-27"},
+		"ref":     {"see A", "see A", "see B", "see A"},
+		"repeat":  {"z,y,z,y", "z,z,y,y", "z,z,x,z", "x,z,y,y"},
+		"sums":    {"90123456789012348 1234567890124 123456780", "90123456789012348 1234567890124 123456780", "90123456789012348 1234567890124 123456780", "90123456789012348 1234567890124 123456780"},
+		"weights": {"big", "big", "big", "big"},
+	}
+	for path := range want {
+		f := newFakes(t, dir, WithSeed(42))
+		for i, expect := range want[path] {
+			if got := fake(t, f, path); got != expect {
+				t.Errorf("%s draw %d = %q, want %q", path, i, got, expect)
+			}
+		}
+	}
+}