1 files changed, 103 insertions, 0 deletions
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/StatsTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/StatsTest.java
new file mode 100644
index 0000000000..6c4b4a4bbd
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+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/StatsTest.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2019, Matthias Sohn <matthias.sohn@sap.com> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class StatsTest {
+	@Test
+	public void testStatsTrivial() {
+		Stats s = new Stats();
+		s.add(1);
+		s.add(1);
+		s.add(1);
+		assertEquals(3, s.count());
+		assertEquals(1.0, s.min(), 1E-6);
+		assertEquals(1.0, s.max(), 1E-6);
+		assertEquals(1.0, s.avg(), 1E-6);
+		assertEquals(0.0, s.var(), 1E-6);
+		assertEquals(0.0, s.stddev(), 1E-6);
+	}
+
+	@Test
+	public void testStats() {
+		Stats s = new Stats();
+		s.add(1);
+		s.add(2);
+		s.add(3);
+		s.add(4);
+		assertEquals(4, s.count());
+		assertEquals(1.0, s.min(), 1E-6);
+		assertEquals(4.0, s.max(), 1E-6);
+		assertEquals(2.5, s.avg(), 1E-6);
+		assertEquals(1.666667, s.var(), 1E-6);
+		assertEquals(1.290994, s.stddev(), 1E-6);
+	}
+
+	@Test
+	/**
+	 * see
+	 * https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Example
+	 */
+	public void testStatsCancellationExample1() {
+		Stats s = new Stats();
+		s.add(1E8 + 4);
+		s.add(1E8 + 7);
+		s.add(1E8 + 13);
+		s.add(1E8 + 16);
+		assertEquals(4, s.count());
+		assertEquals(1E8 + 4, s.min(), 1E-6);
+		assertEquals(1E8 + 16, s.max(), 1E-6);
+		assertEquals(1E8 + 10, s.avg(), 1E-6);
+		assertEquals(30, s.var(), 1E-6);
+		assertEquals(5.477226, s.stddev(), 1E-6);
+	}
+
+	@Test
+	/**
+	 * see
+	 * https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Example
+	 */
+	public void testStatsCancellationExample2() {
+		Stats s = new Stats();
+		s.add(1E9 + 4);
+		s.add(1E9 + 7);
+		s.add(1E9 + 13);
+		s.add(1E9 + 16);
+		assertEquals(4, s.count());
+		assertEquals(1E9 + 4, s.min(), 1E-6);
+		assertEquals(1E9 + 16, s.max(), 1E-6);
+		assertEquals(1E9 + 10, s.avg(), 1E-6);
+		assertEquals(30, s.var(), 1E-6);
+		assertEquals(5.477226, s.stddev(), 1E-6);
+	}
+
+	@Test
+	public void testNoValues() {
+		Stats s = new Stats();
+		assertTrue(Double.isNaN(s.var()));
+		assertTrue(Double.isNaN(s.stddev()));
+		assertTrue(Double.isNaN(s.avg()));
+		assertTrue(Double.isNaN(s.min()));
+		assertTrue(Double.isNaN(s.max()));
+		s.add(42.3);
+		assertTrue(Double.isNaN(s.var()));
+		assertTrue(Double.isNaN(s.stddev()));
+		assertEquals(42.3, s.avg(), 1E-6);
+		assertEquals(42.3, s.max(), 1E-6);
+		assertEquals(42.3, s.min(), 1E-6);
+		s.add(42.3);
+		assertEquals(0, s.var(), 1E-6);
+		assertEquals(0, s.stddev(), 1E-6);
+	}
+}