refactor: always return an Array of results/errors from a plugin pipeline

Always return an `Array` from a pipeline simplify the function utilization as it's more deterministic. Previously, it would return/throw a single value/error when called with a single input and an `Array` of results/errors when called with an `Array` of input.

test/plugins/pipeline.test.js

@@ -18,24 +18,6 @@ test('Execute each function in series passing the same input', async t => {
   t.true(step2.calledBefore(step3));
 });
 
-test('With one step, returns the step values rather than an Array ', async t => {
-  const step1 = stub().resolves(1);
-
-  const result = await pipeline([step1])(0);
-
-  t.deepEqual(result, 1);
-  t.true(step1.calledWith(0));
-});
-
-test('With one step, throws the error rather than an AggregateError ', async t => {
-  const error = new Error('test error 1');
-  const step1 = stub().rejects(error);
-
-  const thrown = await t.throws(pipeline([step1])(0));
-
-  t.is(error, thrown);
-});
-
 test('Execute each function in series passing a transformed input from "getNextInput"', async t => {
   const step1 = stub().resolves(1);
   const step2 = stub().resolves(2);
@@ -96,7 +78,7 @@ test('Execute each function in series calling "transform" to modify the results
   t.deepEqual(getNextInput.args, [[5, 1 + 1], [5, 2 + 1], [5, 3 + 1], [5, 4 + 1]]);
 });
 
-test('Stop execution and throw error is a step rejects', async t => {
+test('Stop execution and throw error if a step rejects', async t => {
   const step1 = stub().resolves(1);
   const step2 = stub().rejects(new Error('test error'));
   const step3 = stub().resolves(3);

test/plugins/plugins.test.js

@@ -143,7 +143,7 @@ test('Merge global options with plugin options', async t => {
     t.context.logger
   );
 
-  const result = await plugins.verifyRelease();
+  const [result] = await plugins.verifyRelease();
 
   t.deepEqual(result.pluginConfig, {localOpt: 'local', globalOpt: 'global', otherOpt: 'locally-defined'});
 });