add optional error message patterns to error test suite

test/error/default_nettype_invalid.sv

+// pattern: bad default_nettype: "invalid"
 `default_nettype invalid
 module top;
     assign foo = 0;

test/error/default_nettype_none.sv

+// pattern: implicit declaration of "foo" but default_nettype is none
 `default_nettype none
 module top;
     assign foo = 0;

test/error/enum_conflict.sv

+// pattern: enum conversion has duplicate vals
 module top;
     typedef enum {
         A = 0,

test/error/highz0_highz1.sv

+// pattern: unexpected token 'highz1'
 module top;
     wire (highz0, highz1) x;
 endmodule

test/error/lhs_expr.sv

+// pattern: cannot convert expression to LHS
 module top;
     logic x;
     assign {<< {x, 2'b00}} = 3'b101;

test/error/lhs_pattern.sv

+// pattern: cannot convert expression to LHS
 module top;
     logic x, y, z;
     assign {<< {x, '{y:y, z:z}}} = 3'b101;

test/error/missing_include.sv

+// pattern: Could not find file "does_not_exist\.sv", included from "missing_include\.sv"
 `include "does_not_exist.sv"

test/error/run.sh

 #!/bin/bash
 
+validateOutput() {
+    stdout_len=`wc -l < $SHUNIT_TMPDIR/stdout`
+    assertEquals "stdout should be empty" 0 $stdout_len
+    stderr=`cat $SHUNIT_TMPDIR/stderr`
+    assertNotNull "stderr should not be empty" "$stderr"
+    line=`head -n1 $1`
+    if [[ "$line" =~ \/\/\ pattern:\ .* ]]; then
+        pattern=${line:12}
+        if [[ ! "$stderr" =~ $pattern ]]; then
+            fail "error message doesn't match\nexpected: $pattern\nactual: $stderr"
+        fi
+    fi
+}
+
 addTest() {
     test=$1
     eval "test_$test() { \
-        $SV2V $test.sv 2> /dev/null > /dev/null; \
+        $SV2V $test.sv 2> $SHUNIT_TMPDIR/stderr > $SHUNIT_TMPDIR/stdout; \
         assertFalse \"conversion should have failed\" \$?; \
+        validateOutput $test.sv; \
     }"
     suite_addTest test_$test
 }

test/error/undefined_macro.sv

+// pattern: Undefined macro: SOMETHING
 `SOMETHING
 module top;
 endmodule

test/error/unmatched_endif.sv

+// pattern: `endif directive outside of an `if/`endif block
 `endif