Runtime compatibility check of loopback version

[bajtos]

Since #14 dropped peer dependency on loopback, there is no mechanism notifying developers when they use incompatible loopback and loopback-testing versions.

We should implement a runtime version check.

[bajtos]

@ritch What if we just wrote a simple version check like this:

  var pkg = require('./package.json');
  var loopbackPkg = require('loopback/package.json');
  var isCompatible = semver.satisfies(loopbackPkg.version, pkg.loopbackVersion);

  if(!isCompatible) {
    throw new Error('incompatible loopback version');
  }

The problem with this check is that loopback must be requireable from loopback-testing, which goes against the current design, where the app/model dependencies are injected by the caller.

Here is what I would like to do instead:

• modify loopback/lib/application.js to provide access to loopback or loopback.version.

• modify loopback/lib/models/mode.js to provide access to loobpack or loopback.version.

• the version checking code will be moved to helpers:

  _beforeEach.withApp = function(app) {
    assertLoopBackVersionIsCompatible(app.loopback.version);
  
    // the original code of `withApp`
  }
  
  // shared by all helpers
  function assertLoopBackVersionIsCompatible(loopbackVersion) {
    var pkg = require('./package.json');
    var isCompatible = semver.satisfies(loopbackVersion, pkg.loopbackVersion);
  
    if(!isCompatible) {
      throw new Error('incompatible loopback version');
    }
  }

Thoughts?