test: added missing Mat22 tests

Author: AlmasB

fxgl-entity/src/test/kotlin/com/almasb/fxgl/physics/box2d/common/Mat22Test.kt

@@ -7,18 +7,64 @@
 package com.almasb.fxgl.physics.box2d.common
 
 import com.almasb.fxgl.core.math.Vec2
-import org.hamcrest.CoreMatchers
 import org.hamcrest.CoreMatchers.*
-import org.hamcrest.MatcherAssert
 import org.hamcrest.MatcherAssert.*
+import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
 
 /**
- *
  * @author Almas Baimagambetov (almaslvl@gmail.com)
  */
 class Mat22Test {
 
+    @Test
+    fun `Set to zero`() {
+        val mat = Mat22()
+
+        mat.ex.set(2f, 3f)
+        mat.ey.set(4f, 7f)
+
+        mat.setZero()
+
+        assertThat(mat.ex, `is`(Vec2()))
+        assertThat(mat.ey, `is`(Vec2()))
+    }
+
+    @Test
+    fun `Invert`() {
+        val A = Mat22()
+        A.ex.set(1f, 2f)
+        A.ey.set(3f, 4f)
+
+        val B = Mat22()
+        A.invertToOut(B)
+
+        val eps = 1e-6f
+        assertEquals(-2.0f, B.ex.x, eps)
+        assertEquals(1.5f, B.ey.x, eps)
+        assertEquals(1.0f, B.ex.y, eps)
+        assertEquals(-0.5f, B.ey.y, eps)
+    }
+
+    @Test
+    fun `Solve Ax = b`() {
+        val A = Mat22()
+        A.ex.set(2.0f, 3.0f)
+        A.ey.set(4.0f, 7.0f)
+
+        val b = Vec2(10.0f, 17.0f)
+        val out = Vec2()
+
+        //    A        x   =   b
+        // [ 2 4 ] x [ 1 ] = [ 10 ]
+        // [ 3 7 ]   [ 2 ]   [ 17 ]
+
+        A.solveToOut(b, out)
+
+        assertEquals(1.0f, out.x, 0.0001f)
+        assertEquals(2.0f, out.y, 0.0001f)
+    }
+
     @Test
     fun `Matrix mul vector`() {
         val mat = Mat22()
@@ -28,7 +74,7 @@ class Mat22Test {
 
         val v = Vec2(1f, 2f)
 
-        // [ 2 4 ] x [ 1 ] = [ 10  ]
+        // [ 2 4 ] x [ 1 ] = [ 10 ]
         // [ 3 7 ]   [ 2 ]   [ 17 ]
 
         val out = Vec2()