Failed to pass tests: "The selected switch default is not installed"

[voodoos]

After building Dune master, test suite fails to execute on my mac.

Failing test is blackbox-tests/test-cases/env/envs-and-contexts.

Steps to reproduce on macOS Mojave 10.14.5:

• Clone ocaml/dune
• Create local switch in cloned dir: opam switch create . 4.09.0 && eval $(opam env)
• Install (some ?) test dependencies: opam install utop base ppx_expect ppx_inline_test odoc menhir
• Run make and make test

Error:

--- a/test/blackbox-tests/test-cases/env/envs-and-contexts/run.t
+++ b/test/blackbox-tests/test-cases/env/envs-and-contexts/run.t.corrected
@@ -1,25 +1,10 @@
 Regression test for https://github.com/ocaml/dune/issues/1016#issuecomment-411390740

   $ dune printenv
-  Environment for context dev:
-
-     ((flags (dev-flags))
-      (ocamlc_flags (-g))
-      (ocamlopt_flags (-g))
-      (c_flags
-       ($flags))
-      (cxx_flags
-       ($flags)))
-
-
-  Environment for context release:
-
-     ((flags (release-flags))
-      (ocamlc_flags (-g))
-      (ocamlopt_flags (-g))
-      (c_flags
-       ($flags))
-      (cxx_flags
-       ($flags)))
-
-
+          opam (internal) (exit 2)
+  /usr/local/bin/opam config env --switch default --sexp --set-switch > /var/folders/qp/fdb35yvx6j1ggk6nww5lg6yr0000gn/T/dune5a1baa.output
+  [ERROR] The selected switch default is not installed.
+          opam (internal) (exit 2)
+  /usr/local/bin/opam config env --switch default --sexp --set-switch > /var/folders/qp/fdb35yvx6j1ggk6nww5lg6yr0000gn/T/dune51660c.output
+  [ERROR] The selected switch default is not installed.
+  [1]

Unsatisfing fix:

Create a global switch named default: opam switch create default ocaml-base-compiler.4.09.0

[rgrinberg]

In the short term, we can disable this test. In the long term, it would be nice to define build contexts entirely within dune workspace files. Once this is possible, we can use this functionality instead of relying on a corresponding opam switch existing.