b2/test/: add first set of substitution tests

b2/test/subfn

@@ -0,0 +1,48 @@
+#!/bin/bash
+. ./Common
+
+###############################################################################
+
+tst "substitutions: F1 -> FN (expand \$\$)" -q F1=foo <<EOF
+!-s
+FN=* { RES=\$\$ }
+EOF
+
+expect <<EOF
+RES=foo
+EOF
+
+#------------------------------------------------------------------------------
+
+tst "substitutions: F2 -> FN (expand \$\$)" -q F1=foo F2=bar <<EOF
+!-s
+FN=?a? { RES=\$\$ }
+EOF
+
+expect <<EOF
+RES=bar
+EOF
+
+#------------------------------------------------------------------------------
+
+tst_fail "substitutions: F* -> FN (expand \$FN)" -q F1=foo <<EOF
+!-s
+FN=* { RES=\$FN }
+EOF
+
+expect <<EOF
+s:2: \$FN may be undefined
+EOF
+
+#------------------------------------------------------------------------------
+
+tst_fail "substitutions: assign to FN" <<EOF
+!-s
+FN=foo
+EOF
+
+expect <<EOF
+s:2: can't assign to pseudo-variable FN
+EOF
+
+###############################################################################