add very basic tests for BuildInterpolator

Tests/PHPCI/Helper/BuildInterpolatorTest.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace PHPCI\Plugin\Tests\Helper;
+
+use PHPCI\Helper\BuildInterpolator;
+use Prophecy\PhpUnit\ProphecyTestCase;
+
+class BuildInterpolatorTest extends ProphecyTestCase
+{
+    /**
+     * @var BuildInterpolator
+     */
+    protected $testedInterpolator;
+
+    protected function setUp()
+    {
+        parent::setup();
+        $this->testedInterpolator = new BuildInterpolator();
+    }
+
+    public function testInterpolate_LeavesStringsUnchangedByDefault()
+    {
+        $string = "Hello World";
+        $expectedOutput = "Hello World";
+
+        $actualOutput = $this->testedInterpolator->interpolate($string);
+
+        $this->assertEquals($expectedOutput, $actualOutput);
+    }
+
+    public function testInterpolate_LeavesStringsUnchangedWhenBuildIsSet()
+    {
+        $build = $this->prophesize('PHPCI\\Model\\Build')->reveal();
+
+        $string = "Hello World";
+        $expectedOutput = "Hello World";
+
+        $this->testedInterpolator->setupInterpolationVars(
+            $build,
+            "/buildpath/",
+            "phpci.com"
+        );
+
+        $actualOutput = $this->testedInterpolator->interpolate($string);
+
+        $this->assertEquals($expectedOutput, $actualOutput);
+    }
+}
+