Throw an error when assertions fail if built from source

Signed-off-by: Nathan Sobo <nathan@github.com>

spec/atom-environment-spec.coffee

@@ -126,6 +126,7 @@ describe "AtomEnvironment", ->
 
     beforeEach ->
       errors = []
+      spyOn(atom, 'isReleasedVersion').andReturn(true)
       atom.onDidFailAssertion (error) -> errors.push(error)
 
     describe "if the condition is false", ->
@@ -147,6 +148,11 @@ describe "AtomEnvironment", ->
           atom.assert(false, "a == b", {foo: 'bar'})
           expect(errors[0].metadata).toEqual {foo: 'bar'}
 
+      describe "when Atom has been built from source", ->
+        it "throws an error", ->
+          atom.isReleasedVersion.andReturn(false)
+          expect(-> atom.assert(false, 'testing')).toThrow('Assertion failed: testing')
+
     describe "if the condition is true", ->
       it "does nothing", ->
         result = atom.assert(true, "a == b")

src/atom-environment.coffee

@@ -840,6 +840,8 @@ class AtomEnvironment extends Model
         error.metadata = callbackOrMetadata
 
     @emitter.emit 'did-fail-assertion', error
+    unless @isReleasedVersion()
+      throw error
 
     false