Add a test checking equations can embed function-built pieces (#1033)

tests/typ/bugs/math-realize.typ

@@ -18,3 +18,30 @@ $ vec(1,2) * 2 $
 $ x^2 #hide[$(>= phi.alt) union y^2 0$] z^2 $
 Hello #hide[there $x$]
 and #hide[$ f(x) := x^2 $]
+
+---
+// Test equations can embed equation pieces built by functions
+#let foo(v1, v2) = {
+  // Return an equation piece that would've been rendered in
+  // inline style if the piece is not embedded
+  $v1 v2^2$
+}
+#let bar(v1, v2) = {
+  // Return an equation piece that would've been rendered in
+  // block style if the piece is not embedded
+  $ v1 v2^2 $
+}
+#let baz(..sink) = {
+  // Return an equation piece built by joining arrays
+  sink.pos().map(x => $hat(#x)$).join(sym.and)
+}
+
+Inline $2 foo(alpha, (M+foo(a, b)))$.
+
+Inline $2 bar(alpha, (M+foo(a, b)))$.
+
+Inline $2 baz(x,y,baz(u, v))$.
+
+$ 2 foo(alpha, (M+foo(a, b))) $
+$ 2 bar(alpha, (M+foo(a, b))) $
+$ 2 baz(x,y,baz(u, v)) $