Add test for ocaml#5926

NV_VARS10 should be a:b and NV_VARS11 should be b:a (no leading colon)

tests/reftests/env.test

@@ -89,6 +89,12 @@ setenv: [
   [ NV_VARS8 =+ "foo" ]
   [ NV_VARS9 = ""     ]
   [ NV_VARS9 =: "foo" ]
+  [ NV_VARS10 := "a"  ]
+  [ NV_VARS10 =: "b"  ]
+  [ NV_VARS11 =: "a"  ]
+  [ NV_VARS11 := "b"  ]
+  [ NV_VARS12 := "a"  ]
+  [ NV_VARS13 =: "b"  ]
 ]
 flags: compiler
 ### opam switch create emptyvar nv
@@ -101,6 +107,10 @@ Switch invariant: ["nv"]
 Done.
 ### opam exec -- env | grep "NV_VARS" | ';' -> ':'
 NV_VARS=
+NV_VARS10=:a:b
+NV_VARS11=:b:a
+NV_VARS12=a:
+NV_VARS13=:b
 NV_VARS3=foo:
 NV_VARS4=
 NV_VARS6=foo:
@@ -114,19 +124,31 @@ NV_VARS6='foo:': export NV_VARS6:
 NV_VARS7='foo:': export NV_VARS7:
 NV_VARS8=':foo': export NV_VARS8:
 NV_VARS9=':foo': export NV_VARS9:
+NV_VARS10=':a:b': export NV_VARS10:
+NV_VARS11=':b:a': export NV_VARS11:
+NV_VARS12='a:': export NV_VARS12:
+NV_VARS13=':b': export NV_VARS13:
 ### opam exec -- opam env --revert | grep "NV_VARS" | ';' -> ':'
 NV_VARS3='': export NV_VARS3:
 NV_VARS4='': export NV_VARS4:
 NV_VARS6='': export NV_VARS6:
 NV_VARS7='': export NV_VARS7:
 NV_VARS8='': export NV_VARS8:
 NV_VARS9='': export NV_VARS9:
+NV_VARS10='': export NV_VARS10:
+NV_VARS11='': export NV_VARS11:
+NV_VARS12='': export NV_VARS12:
+NV_VARS13='': export NV_VARS13:
 ### NV_VARS=/another/path
 ### NV_VARS2=/another/different/path
 ### NV_VARS3=/yet/another/different/path
 ### NV_VARS4=ignored-value
 ### opam exec -- env | grep "NV_VARS" | ';' -> ':'
 NV_VARS=/another/path
+NV_VARS10=:a:b
+NV_VARS11=:b:a
+NV_VARS12=a:
+NV_VARS13=:b
 NV_VARS2=/another/different/path
 NV_VARS3=foo:/yet/another/different/path
 NV_VARS4=
@@ -141,13 +163,21 @@ NV_VARS6='foo:': export NV_VARS6:
 NV_VARS7='foo:': export NV_VARS7:
 NV_VARS8=':foo': export NV_VARS8:
 NV_VARS9=':foo': export NV_VARS9:
+NV_VARS10=':a:b': export NV_VARS10:
+NV_VARS11=':b:a': export NV_VARS11:
+NV_VARS12='a:': export NV_VARS12:
+NV_VARS13=':b': export NV_VARS13:
 ### opam exec -- opam env --revert | grep "NV_VARS" | ';' -> ':'
 NV_VARS3='/yet/another/different/path': export NV_VARS3:
 NV_VARS4='': export NV_VARS4:
 NV_VARS6='': export NV_VARS6:
 NV_VARS7='': export NV_VARS7:
 NV_VARS8='': export NV_VARS8:
 NV_VARS9='': export NV_VARS9:
+NV_VARS10='': export NV_VARS10:
+NV_VARS11='': export NV_VARS11:
+NV_VARS12='': export NV_VARS12:
+NV_VARS13='': export NV_VARS13:
 ### : Full revert of uninstalled package with setenv :
 ### <pkg:foo.1>
 opam-version: "2.0"
@@ -207,6 +237,10 @@ NV_VARS6='foo:': export NV_VARS6:
 NV_VARS7='foo:': export NV_VARS7:
 NV_VARS8=':foo': export NV_VARS8:
 NV_VARS9=':foo': export NV_VARS9:
+NV_VARS10=':a:b': export NV_VARS10:
+NV_VARS11=':b:a': export NV_VARS11:
+NV_VARS12='a:': export NV_VARS12:
+NV_VARS13=':b': export NV_VARS13:
 ### OPAMNOENVNOTICE=1
 ### : Env hooks :
 ### <pkg:av.1>