diff --git a/solve-classic/src/commonTest/kotlin/it/unibo/tuprolog/solve/systemtest/TestClassicIs.kt b/solve-classic/src/commonTest/kotlin/it/unibo/tuprolog/solve/systemtest/TestClassicIs.kt
new file mode 100644
index 000000000..43772d62d
--- /dev/null
+++ b/solve-classic/src/commonTest/kotlin/it/unibo/tuprolog/solve/systemtest/TestClassicIs.kt
@@ -0,0 +1,40 @@
+package it.unibo.tuprolog.solve.systemtest
+
+import it.unibo.tuprolog.solve.ClassicSolverFactory
+import it.unibo.tuprolog.solve.SolverFactory
+import it.unibo.tuprolog.solve.TestIs
+import kotlin.test.Test
+
+class TestClassicIs : TestIs, SolverFactory by ClassicSolverFactory  {
+    private val prototype = TestIs.prototype(this)
+
+    @Test
+    override fun testIsResult() {
+        prototype.testIsResult()
+    }
+
+    @Test
+    override fun testIsXY(){
+        prototype.testIsXY()
+    }
+
+    @Test
+    override fun testIsFoo() {
+        prototype.testIsFoo()
+    }
+
+    @Test
+    override fun testIsNNumber() {
+        prototype.testIsNNumber()
+    }
+
+    @Test
+    override fun testIsNumberFoo() {
+        prototype.testIsNumberFoo()
+    }
+
+    @Test
+    override fun testIsXFloat() {
+        prototype.testIsXFloat()
+    }
+}
\ No newline at end of file
diff --git a/solve-streams/src/commonTest/kotlin/it/unibo/tuprolog/solve/systemtest/TestStreamsIs.kt b/solve-streams/src/commonTest/kotlin/it/unibo/tuprolog/solve/systemtest/TestStreamsIs.kt
new file mode 100644
index 000000000..12455e9d1
--- /dev/null
+++ b/solve-streams/src/commonTest/kotlin/it/unibo/tuprolog/solve/systemtest/TestStreamsIs.kt
@@ -0,0 +1,40 @@
+package it.unibo.tuprolog.solve.systemtest
+
+import it.unibo.tuprolog.solve.StreamsSolverFactory
+import it.unibo.tuprolog.solve.SolverFactory
+import it.unibo.tuprolog.solve.TestIs
+import kotlin.test.Test
+
+class TestStreamsIs : TestIs, SolverFactory by StreamsSolverFactory  {
+    private val prototype = TestIs.prototype(this)
+
+    @Test
+    override fun testIsResult() {
+        prototype.testIsResult()
+    }
+
+    @Test
+    override fun testIsXY(){
+        prototype.testIsXY()
+    }
+
+    @Test
+    override fun testIsFoo() {
+        prototype.testIsFoo()
+    }
+
+    @Test
+    override fun testIsNNumber() {
+        prototype.testIsNNumber()
+    }
+
+    @Test
+    override fun testIsNumberFoo() {
+        prototype.testIsNumberFoo()
+    }
+
+    @Test
+    override fun testIsXFloat() {
+        prototype.testIsXFloat()
+    }
+}
\ No newline at end of file
diff --git a/test-solve/src/commonMain/kotlin/it/unibo/tuprolog/solve/TestIs.kt b/test-solve/src/commonMain/kotlin/it/unibo/tuprolog/solve/TestIs.kt
new file mode 100644
index 000000000..20184b937
--- /dev/null
+++ b/test-solve/src/commonMain/kotlin/it/unibo/tuprolog/solve/TestIs.kt
@@ -0,0 +1,67 @@
+package it.unibo.tuprolog.solve
+
+interface TestIs : SolverTest {
+    companion object {
+        fun prototype(solverFactory: SolverFactory): TestIs =
+            TestIsImpl(solverFactory)
+    }
+
+    /**
+     * Tests the queries
+     * ```prolog
+     * ?- 'is'(Result,3 + 11.0).
+     * ```
+     * succeeds on a solver initialized with default built-ins and with and empty theory,
+     * producing 1 solution which binds variable `Result` to `14.0`.
+     */
+    fun testIsResult()
+
+    /**
+     * Tests the queries
+     * ```prolog
+     * ?- (X = 1 + 2, 'is'(Y, X * 3)).
+     * ```
+     * succeeds on a solver initialized with default built-ins and with and empty theory,
+     * producing 2 solutions which binds variable `X` to `1+2` and `Y` to `9`.
+     */
+    fun testIsXY()
+
+    /**
+     * Tests the queries
+     * ```prolog
+     * ?- 'is'(foo,77).
+     * ```
+     * fails on a solver initialized with default built-ins and with and empty theory,
+     */
+    fun testIsFoo()
+
+    /**
+     * Tests the queries
+     * ```prolog
+     * ?- 'is'(77, N).
+     * ```
+     * fails on a solver initialized with default built-ins and with and empty theory,
+     * producing exception `instantiation_error`.
+     */
+    fun testIsNNumber()
+
+    /**
+     * Tests the queries
+     * ```prolog
+     * ?- 'is'(77, foo).
+     * ```
+     * fails on a solver initialized with default built-ins and with and empty theory,
+     * producing exception `type_error(foo/0)`.
+     */
+    fun testIsNumberFoo()
+
+    /**
+     * Tests the queries
+     * ```prolog
+     * ?- 'is'(X,float(3)).
+     * ```
+     * succeeds on a solver initialized with default built-ins and with and empty theory,
+     * producing 1 solution which binds variable `X` to `3.0`.
+     */
+    fun testIsXFloat()
+}
\ No newline at end of file
diff --git a/test-solve/src/commonMain/kotlin/it/unibo/tuprolog/solve/TestIsImpl.kt b/test-solve/src/commonMain/kotlin/it/unibo/tuprolog/solve/TestIsImpl.kt
new file mode 100644
index 000000000..33186d5d2
--- /dev/null
+++ b/test-solve/src/commonMain/kotlin/it/unibo/tuprolog/solve/TestIsImpl.kt
@@ -0,0 +1,109 @@
+package it.unibo.tuprolog.solve
+
+import it.unibo.tuprolog.dsl.theory.prolog
+import it.unibo.tuprolog.solve.exception.error.InstantiationError
+import it.unibo.tuprolog.solve.exception.error.TypeError
+
+internal class TestIsImpl(private val solverFactory: SolverFactory) : TestIs {
+    override fun testIsResult() {
+        prolog {
+            val solver = solverFactory.solverWithDefaultBuiltins()
+
+            val query = "Result" `is` numOf(3) + 11.0
+            val solutions = solver.solve(query, mediumDuration).toList()
+
+            assertSolutionEquals(
+                kotlin.collections.listOf(query.yes("Result" to 14.0)),
+                solutions
+            )
+        }
+    }
+
+    override fun testIsXY() {
+        prolog {
+            val solver = solverFactory.solverWithDefaultBuiltins()
+
+            val query = ("X" `=` numOf(1) + 2) and ("Y" `is` "X" * 3)
+            val solutions = solver.solve(query, mediumDuration).toList()
+
+            assertSolutionEquals(
+                kotlin.collections.listOf(query.yes("X" to numOf(1)+2, "Y" to 9)),
+                solutions
+            )
+        }
+    }
+
+    override fun testIsFoo() {
+        prolog {
+            val solver = solverFactory.solverWithDefaultBuiltins()
+
+            val query = "foo" `is` 77
+            val solutions = solver.solve(query, mediumDuration).toList()
+
+            assertSolutionEquals(
+                kotlin.collections.listOf(query.no()),
+                solutions
+            )
+        }
+    }
+
+    override fun testIsNNumber() {
+        prolog {
+            val solver = solverFactory.solverWithDefaultBuiltins()
+
+            val query = 77 `is` "N"
+            val solutions = solver.solve(query, mediumDuration).toList()
+
+            assertSolutionEquals(
+                kotlin.collections.listOf(
+                    query.halt(
+                        InstantiationError.forGoal(
+                            DummyInstances.executionContext,
+                            Signature("is", 2),
+                            varOf("N")
+                        )
+                    )
+                ),
+                solutions
+            )
+        }
+    }
+
+    override fun testIsNumberFoo() {
+        prolog {
+            val solver = solverFactory.solverWithDefaultBuiltins()
+
+            val query = 77 `is` "foo"
+            val solutions = solver.solve(query, mediumDuration).toList()
+
+            assertSolutionEquals(
+                kotlin.collections.listOf(
+                    query.halt(
+                        TypeError.forGoal(
+                            DummyInstances.executionContext,
+                            Signature("is", 2),
+                            TypeError.Expected.EVALUABLE,
+                            atomOf("foo")
+
+                        )
+                    )
+                ),
+                solutions
+            )
+        }
+    }
+
+    override fun testIsXFloat() {
+        prolog {
+            val solver = solverFactory.solverWithDefaultBuiltins()
+
+            val query = "X" `is` float(3)
+            val solutions = solver.solve(query, mediumDuration).toList()
+
+            assertSolutionEquals(
+                kotlin.collections.listOf(query.yes("X" to 3.0)),
+                solutions
+            )
+        }
+    }
+}
\ No newline at end of file