feat: allow env variables to overwrite smtp config

Fixes #3

test/Common.spec.ts

@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2019 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+import { expect } from 'chai';
+import { slow, suite, test, timeout } from 'mocha-typescript';
+import { deleteUndefinedProperties } from '../src/common';
+
+@suite(timeout(2000), slow(1000))
+export class CommonSpec {
+  /* tslint:disable:member-ordering */
+  @test
+  deleteUndefinedProperties1() {
+    expect(deleteUndefinedProperties(
+      {
+        a: 2,
+        b: {
+          c: 3,
+          d: undefined,
+        },
+      },
+    )).to.deep.equal(
+      {
+        a: 2,
+        b: {
+          c: 3,
+        },
+      },
+    );
+  }
+
+  @test
+  deleteUndefinedProperties2() {
+    expect(deleteUndefinedProperties(
+      {
+        a: undefined,
+        b: undefined,
+      },
+    )).to.deep.equal(
+      {},
+    );
+  }
+
+  @test
+  deleteUndefinedProperties3() {
+    expect(deleteUndefinedProperties(
+      {
+        a: 2,
+        b: 'foo',
+        c: 'bar',
+      },
+    )).to.deep.equal(
+      {
+        a: 2,
+        b: 'foo',
+        c: 'bar',
+      },
+    );
+  }
+}