Add scenario (yarn) tests for most of branching and merging

These scenarios test the basics of most of the subcommands the
branch and merge plugin provides. They don't purport to be complete,
but give some indication that things work, and form a basis upon
which further things can be built. Yarn also isn't included in a
Baserock release yet, so we need to keep the cmdtests until Baserock
10 has been released.

The existing cmdtest tests are not modified by this: they are left
intact, until they can analysed in detail for things to be added to
the scenarios. After that, the cmdtest tests will start to go away.

Merging is not covered by these tests: it is not clear how merge should
work, and the current code is known to do the wrong thing in many cases.
Scenarios for merge will be added later.

Building is also not covered. Testing builds well needs some additional,
careful thinking, and that isn't ready for this patch series. It will
be added later.

1 files changed, 283 insertions, 0 deletions

diff --git a/yarns/branches-workspaces.yarn b/yarns/branches-workspaces.yarn
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+Morph black box tests for system branches and workspaces
+========================================================
+
+Morph implements **system branches**, which are checked out and
+manipulated by the user in **workspaces**. See
+FIXME for more information.
+
+Workspace creation
+------------------
+
+The first thing a user needs to do is create a workspace.
+
+    SCENARIO    create and initialise a new workspace
+    GIVEN       no workspace
+    WHEN        morph initialises a workspace
+    THEN        an empty workspace exists
+
+The workspace directory may exist, if it is empty.
+
+    SCENARIO    initialise an empty workspace directory
+    GIVEN       an empty workspace directory
+    WHEN        morph initialises a workspace
+    THEN        an empty workspace exists
+
+However, the directory must really be empty. It must not be
+an empty, but initialised workspace.
+
+    SCENARIO    initialise an existing, empty workspace directory
+    GIVEN       no workspace
+    WHEN        morph initialises a workspace
+    AND         morph attempts to initialise a workspace
+    THEN        morph failed
+
+Likewise, if the directory exists, and is non-empty, but isn't an
+existing workspace, initialising it should fail.
+
+    SCENARIO    initialise a non-empty workspace directory
+    GIVEN       a non-empty workspace directory
+    WHEN        morph attempts to initialise a workspace
+    THEN        morph failed
+
+Checking out or branching system branches
+-----------------------------------------
+
+Once we have a workspace, we can check out a system branch.
+
+    SCENARIO    check out an existing system branch
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        checking out the master system branch
+    THEN        the system branch master is checked out
+
+Checking out a system branch should fail, if the branch doesn't exist.
+
+    SCENARIO    checking out a system branch that doesn't exist
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        morph attempts to check out system branch foo
+    THEN        morph failed
+
+We can, instead, create a new system branch, off master.
+
+    SCENARIO    branch off master
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        creating system branch foo
+    THEN        the system branch foo is checked out
+
+We can also branch off another system branch. However, we need to first
+push the other branch to the git server, since Morph is not smart enough
+to check for that locally.
+
+    SCENARIO    branch off non-master
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        creating system branch foo
+    AND         pushing system branch foo to git server
+    AND         creating system branch bar, based on foo
+    THEN        the system branch bar is checked out
+
+Query commands in workspaces
+----------------------------
+
+`morph workspace` writes out the fully qualified path to the workspace
+directory, regardless of where the user is. There's a few cases.
+
+    SCENARIO    morph workspace works at root of empty workspace
+    GIVEN       a workspace
+    WHEN        morph reports workspace in .
+    THEN        workspace is reported correctly
+
+Also check it in the root of a system branch checkout, and inside
+a git checkout inside that.
+
+    SCENARIO    morph workspace works in system branch checkouts
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        checking out the master system branch
+    AND         morph reports workspace in master
+    THEN        workspace is reported correctly
+
+We leak a little bit of the implementation here, to keep things simple:
+the (mocked) git server the implementation sets up has the `test:morphs`
+repository, which is the system branch root repository.
+
+    WHEN        morph reports workspace in master/test:morphs
+    THEN        workspace is reported correctly
+
+However, running it outside a workspace should fail.
+
+    SCENARIO    morph fails outside workspace
+    GIVEN       no workspace
+    WHEN        morph attempts to report workspace
+    THEN        morph failed
+
+`morph show-system-branch` should report the name of the system
+branch, when run anywhere in the system branch checkout. As a special
+case, if there is only one system branch checkout at or below the
+current working directory, it will find it and report it correctly.
+
+    SCENARIO    morph reports system branch
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        checking out the master system branch
+    AND         reporting system branch in master
+    THEN        system branch is reported as master
+
+    WHEN        reporting system branch in master/test:morphs
+    THEN        system branch is reported as master
+
+    WHEN        reporting system branch  in .
+    THEN        system branch is reported as master
+
+However, if there's two system branches checked out below the
+current directory, things should fail.
+
+    SCENARIO    morph fails to report system branch with two checked out
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        checking out the master system branch
+    AND         creating system branch foo
+    AND         attempting to report system branch in .
+    THEN        morph failed
+
+`morph show-branch-root` reports the URL (possibly aliases) of the
+system branch root repository. It can be run inside a checkout, or
+somewhere outside a checkout, where exactly one checkout exists below.
+
+    SCENARIO    morph reports system branch root repository
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        checking out the master system branch
+    AND         reporting system branch root repository in master
+    THEN        root repository is reported as test:morphs
+
+    WHEN        reporting system branch root repository in .
+    THEN        root repository is reported as test:morphs
+
+However, it fails if run outside a checkout and there's no system
+branches checked out.
+
+    SCENARIO    morph fails to report system branch with two checked out
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        attempting to report system branch root repository in .
+    THEN        morph failed
+
+Editing components
+------------------
+
+`morph edit` can edit refs for a stratum only, or it can do that for
+a chunk, and check out the chunk's repository.
+
+First of all, we verify that that when we create a system branch,
+all the refs are unchanged.
+
+    SCENARIO    morph branch does not edit refs
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        creating system branch foo
+    THEN        in branch foo, system test-system refs test-stratum in master
+    AND         in branch foo, stratum test-stratum refs test-chunk in master
+
+Then edit the stratum.
+
+    WHEN    editing stratum test-stratum in system test-system in branch foo
+    THEN    in branch foo, system test-system refs test-stratum in foo
+
+Edit the chunk. We make use of special knowledge here: `test:test-chunk`
+is a chunk repository created in the mocked git server, for testing
+purposes.
+
+    WHEN editing chunk test-chunk in test-stratum in test-system in branch foo
+    THEN in branch foo, system test-system refs test-stratum in foo
+    AND  in branch foo, stratum test-stratum refs test-chunk in foo
+    AND  edited chunk test:test-chunk has git branch foo
+
+Status of system branch checkout
+--------------------------------
+
+`morph status` shows the status of all git repositories in a
+system branch checkout: only the ones that exist locally, not all the
+repositories referenced in the system branch.
+
+    SCENARIO    morph status reports changes correctly
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        creating system branch foo
+    THEN        morph reports no outstanding changes in foo
+
+    WHEN editing stratum test-stratum in system test-system in branch foo
+    THEN morph reports changes in foo in test:morphs only
+
+    WHEN editing chunk test-chunk in test-stratum in test-system in branch foo
+    THEN morph reports changes in foo in test:morphs only
+
+    WHEN        creating file foo in test:test-chunk in branch foo
+    THEN        morph reports changes in foo in test:morphs only
+
+    WHEN        adding file foo in test:test-chunk in branch foo to git
+    THEN        morph reports changes in foo in test:morphs and test:test-chunk
+
+    WHEN        committing changes in test:morphs in branch foo
+    THEN        morph reports changes in foo in test:test-chunk only
+
+    WHEN        committing changes in test:test-chunk in branch foo
+    THEN        morph reports no outstanding changes in foo
+
+`morph foreach`
+--------------
+
+`morph foreach` runs a shell command in each of the git repos in a system
+branch checkout.
+
+    SCENARIO morph foreach runs command in each git repo
+    GIVEN a workspace
+    AND   a git server
+    WHEN  creating system branch foo
+    AND   editing chunk test-chunk in test-stratum in test-system in branch foo
+    AND   running shell command in each repo in foo
+    THEN  morph ran command in test:morphs in foo
+    AND   morph ran command in test:test-chunk in foo
+
+Explicit petrification
+----------------------
+
+We petrify branches explicitly (though this may later change so that
+`morph branch` does it automatically). To test this, we create a branch,
+petrify it, and verify that every ref looks like a SHA1. We then
+unpetrify and verify that we have all the same refs as before.
+
+    SCENARIO    morph petrifies and unpetrifies
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        creating system branch foo
+    AND         pushing system branch foo to git server
+    AND         remembering all refs in foo
+    AND         petrifying foo
+    THEN        foo is petrified
+    WHEN        unpetrifying foo
+    THEN        foo refs are as remembered
+
+Tagging system branches
+-----------------------
+
+`morph tag` creates a git tag in the system branch's root repository,
+and a petrified commit the tag refers to. It does not petrify the
+system branch itself, only the tag.
+
+    SCENARIO    morph tags a system branch
+    GIVEN       a workspace
+    AND         a git server
+    WHEN        creating system branch foo
+    AND         tagging system branch foo as test123
+    THEN        morph tag test123 in foo is an annotated git tag
+    AND         morph tag test123 in foo refers to a petrified commit
+    AND         foo is not petrified
+
+Creating a tag twice should fail.
+
+    WHEN        attempting to tag system branch foo as test123
+    THEN        morph failed
+