add assertion for accidental non-base blueprint

Author: Kelly Selden

src/get-start-and-end-commands.js

@@ -21,6 +21,10 @@ module.exports = function getStartAndEndCommands({
   startBlueprint,
   endBlueprint
 }) {
+  if (baseBlueprint && !baseBlueprint.isBaseBlueprint) {
+    throw new Error('The intended base blueprint is not actually a base blueprint.');
+  }
+
   if (endBlueprint.isBaseBlueprint && baseBlueprint) {
     throw new Error('You supplied two layers of base blueprints.');
   }

test/unit/get-start-and-end-commands-test.js

@@ -56,6 +56,14 @@ describe(_getStartAndEndCommands, function() {
     }, options));
   }
 
+  it('throws if base blueprint is not marked as such', function() {
+    let f = () => getStartAndEndCommands({
+      baseBlueprint: {}
+    });
+
+    expect(f).to.throw('The intended base blueprint is not actually a base blueprint.');
+  });
+
   it('throws if two layers of base blueprints', function() {
     let f = () => getStartAndEndCommands({
       baseBlueprint