test-config: add tests for invalid syntax

This was not tested and there is more to come in the next patch.

tests/test-config.t

@@ -1,44 +1,66 b''
 hide outer repo
   $ hg init
 
+Invalid syntax: no value
+
+  $ cat > .hg/hgrc << EOF
+  > novaluekey
+  > EOF
+  $ hg showconfig
+  hg: parse error at $TESTTMP/.hg/hgrc:1: novaluekey
+  [255]
+
+Invalid syntax: no key
+
+  $ cat > .hg/hgrc << EOF
+  > =nokeyvalue
+  > EOF
+  $ hg showconfig
+  hg: parse error at $TESTTMP/.hg/hgrc:1: =nokeyvalue
+  [255]
+
+Reset hgrc
+
+  $ echo > .hg/hgrc
+
 Test case sensitive configuration
 
   $ echo '[Section]' >> $HGRCPATH
   $ echo 'KeY = Case Sensitive' >> $HGRCPATH
   $ echo 'key = lower case' >> $HGRCPATH
 
   $ hg showconfig Section
   Section.KeY=Case Sensitive
   Section.key=lower case
 
 Test "%unset"
 
   $ cat >> $HGRCPATH <<EOF
   > [unsettest]
   > local-hgrcpath = should be unset (HGRCPATH)
   > %unset local-hgrcpath
   > 
   > global = should be unset (HGRCPATH)
   > 
   > both = should be unset (HGRCPATH)
   > 
   > set-after-unset = should be unset (HGRCPATH)
   > EOF
 
   $ cat >> .hg/hgrc <<EOF
   > [unsettest]
   > local-hgrc = should be unset (.hg/hgrc)
   > %unset local-hgrc
   > 
   > %unset global
   > 
   > both = should be unset (.hg/hgrc)
   > %unset both
   > 
   > set-after-unset = should be unset (.hg/hgrc)
   > %unset set-after-unset
   > set-after-unset = should be set (.hg/hgrc)
   > EOF
 
   $ hg showconfig unsettest
   unsettest.set-after-unset=should be set (.hg/hgrc)