1 files changed, 79 insertions, 0 deletions
diff --git a/tests/phpunit/includes/libs/RunningStatTest.php b/tests/phpunit/includes/libs/RunningStatTest.php
new file mode 100644
index 00000000..dc5db82c
--- /dev/null
+++ b/tests/phpunit/includes/libs/RunningStatTest.php
@@ -0,0 +1,79 @@
+<?php
+/**
+ * PHP Unit tests for RunningStat class.
+ * @covers RunningStat
+ */
+class RunningStatTest extends MediaWikiTestCase {
+
+	public $points = array(
+		49.7168, 74.3804,  7.0115, 96.5769, 34.9458,
+		36.9947, 33.8926, 89.0774, 23.7745, 73.5154,
+		86.1322, 53.2124, 16.2046, 73.5130, 10.4209,
+		42.7299, 49.3330, 47.0215, 34.9950, 18.2914,
+	);
+
+	/**
+	 * Verify that the statistical moments and extrema computed by RunningStat
+	 * match expected values.
+	 * @covers RunningStat::push
+	 * @covers RunningStat::count
+	 * @covers RunningStat::getMean
+	 * @covers RunningStat::getVariance
+	 * @covers RunningStat::getStdDev
+	 */
+	public function testRunningStatAccuracy() {
+		$rstat = new RunningStat();
+		foreach( $this->points as $point ) {
+			$rstat->push( $point );
+		}
+
+		$mean = array_sum( $this->points ) / count( $this->points );
+		$variance = array_sum( array_map( function ( $x ) use ( $mean ) {
+			return pow( $mean - $x, 2 );
+		}, $this->points ) ) / ( count( $rstat ) - 1 );
+		$stddev = sqrt( $variance );
+
+		$this->assertEquals( count( $rstat ), count( $this->points ) );
+		$this->assertEquals( $rstat->min, min( $this->points ) );
+		$this->assertEquals( $rstat->max, max( $this->points ) );
+		$this->assertEquals( $rstat->getMean(), $mean );
+		$this->assertEquals( $rstat->getVariance(), $variance );
+		$this->assertEquals( $rstat->getStdDev(), $stddev );
+	}
+
+	/**
+	 * When one RunningStat instance is merged into another, the state of the
+	 * target RunningInstance should have the state that it would have had if
+	 * all the data had been accumulated by it alone.
+	 * @covers RunningStat::merge
+	 * @covers RunningStat::count
+	 */
+	public function testRunningStatMerge() {
+		$expected = new RunningStat();
+
+		foreach( $this->points as $point ) {
+			$expected->push( $point );
+		}
+
+		// Split the data into two sets
+		$sets = array_chunk( $this->points, floor( count( $this->points ) / 2 ) );
+
+		// Accumulate the first half into one RunningStat object
+		$first = new RunningStat();
+		foreach( $sets[0] as $point ) {
+			$first->push( $point );
+		}
+
+		// Accumulate the second half into another RunningStat object
+		$second = new RunningStat();
+		foreach( $sets[1] as $point ) {
+			$second->push( $point );
+		}
+
+		// Merge the second RunningStat object into the first
+		$first->merge( $second );
+
+		$this->assertEquals( count( $first ), count( $this->points ) );
+		$this->assertEquals( $first, $expected );
+	}
+}