diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AndOr.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AndOr.jet
new file mode 100644
index 00000000000..a2272cfd94c
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AndOr.jet
@@ -0,0 +1,12 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    if (x != null && bar(x) == 0) bar(bar(x))
+    bar(<!TYPE_MISMATCH!>x<!>)
+    if (x == null || bar(x) == 0) bar(bar(<!TYPE_MISMATCH!>x<!>))
+    bar(<!TYPE_MISMATCH!>x<!>)
+    if (x is Int && bar(x)*bar(x) == bar(x)) bar(x)
+    bar(<!TYPE_MISMATCH!>x<!>)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayAccess.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayAccess.jet
new file mode 100644
index 00000000000..3d178c3f5dd
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayAccess.jet
@@ -0,0 +1,13 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+    val a = Array<Int>(3, {0})
+
+    if (x != null) bar(a[x]) else bar(a<!NO_GET_METHOD!>[<!TYPE_MISMATCH!>x<!>]<!>)
+    bar(a[if (x == null) 0 else x])
+    bar(a<!NO_GET_METHOD!>[<!TYPE_MISMATCH!>x<!>]<!>)
+    
+    "123"<!NO_GET_METHOD!>[<!TYPE_MISMATCH!>x<!>]<!>;
+    if (x != null) "123"[x];
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpression.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpression.jet
new file mode 100644
index 00000000000..e64572a063c
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/BinaryExpression.jet
@@ -0,0 +1,9 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    bar(1 + (if (x == null) 0 else x))
+    bar(if (x == null) <!TYPE_MISMATCH!>x<!> else x)
+    if (x != null) bar(x + x/(x-x*x))
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/DeepIf.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/DeepIf.jet
new file mode 100644
index 00000000000..5373ed1f4d4
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/DeepIf.jet
@@ -0,0 +1,30 @@
+fun bar(x: Int) = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    if (x != null) {
+        bar(x)
+        if (x != null) {
+            bar(x)
+            if (1 < 2) bar(x)
+            if (1 > 2) bar(x)
+        }
+        if (x == null) {
+            bar(x)
+        }
+        if (x == null) bar(x) else bar(x)
+        bar(bar(x))
+    } else if (x == null) {
+        bar(<!TYPE_MISMATCH!>x<!>)
+        if (x != null) {
+            bar(x)
+            if (x == null) bar(x)
+            if (x == null) bar(x) else bar(x)
+            bar(bar(x) + bar(x))
+        } else if (x == null) {
+            bar(<!TYPE_MISMATCH!>x<!>)
+        }
+    }
+
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/DoWhile.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/DoWhile.jet
new file mode 100644
index 00000000000..7117aeb2c1c
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/DoWhile.jet
@@ -0,0 +1,16 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    do {
+        bar(<!TYPE_MISMATCH!>x<!>)
+    } while (x == null)
+    bar(x)
+    
+    val y: Int? = null
+    do {
+        bar(<!TYPE_MISMATCH!>y<!>)
+    } while (y != null)
+    bar(<!TYPE_MISMATCH!>y<!>)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Elvis.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Elvis.jet
new file mode 100644
index 00000000000..fcfdbb7b7b7
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Elvis.jet
@@ -0,0 +1,9 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    bar(x ?: 0)
+    if (x != null) bar(x ?: x)
+    bar(<!TYPE_MISMATCH!>x<!>)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ExclExcl.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ExclExcl.jet
new file mode 100644
index 00000000000..94d44069aec
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ExclExcl.jet
@@ -0,0 +1,13 @@
+fun bar(x: Int) = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    bar(<!TYPE_MISMATCH!>x<!>)
+    if (x != null) bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
+    if (x == null) bar(x!!)
+    if (x != null) else bar(x!!)
+    if (x == null) else bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
+    if (x != null) bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>) else bar(x!!)
+    if (x == null) bar(x!!) else bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/For.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/For.jet
new file mode 100644
index 00000000000..aa1ef31839c
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/For.jet
@@ -0,0 +1,24 @@
+import java.util.HashMap
+
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+    val a = Array<Int>(3, {0})
+
+    for (p in a) {
+        bar(<!TYPE_MISMATCH!>x<!>)
+        if (x == null) continue
+        bar(x)
+        for (q in a) {
+            bar(x)
+            if (x == null) bar(x)
+        }
+    }
+
+    for (p in a) {
+        bar(<!TYPE_MISMATCH!>x<!>)
+        if (x == null) break
+        bar(x)
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/FunctionLiteral.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/FunctionLiteral.jet
new file mode 100644
index 00000000000..b78bfc8489f
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/FunctionLiteral.jet
@@ -0,0 +1,9 @@
+fun bar(x: Int) = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    fun baz() = bar(<!TYPE_MISMATCH!>x<!>)
+    fun quux() = if (x != null) bar(x) else baz()
+    fun quuux() = bar(if (x == null) 0 else x)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/IfThenElse.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/IfThenElse.jet
new file mode 100644
index 00000000000..bc1e14b7dab
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/IfThenElse.jet
@@ -0,0 +1,30 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    bar(if (x == null) 0 else x)
+
+    if (x == null) {
+        bar(<!TYPE_MISMATCH!>x<!>)
+        return
+    } else {
+        bar(x)
+    }
+    bar(x)
+
+    val y: Int? = null
+    if (y is Int) {
+        bar(y)
+    } else {
+        bar(<!TYPE_MISMATCH!>y<!>)
+        return
+    }
+    bar(y)
+
+    val z: Int? = null
+    if (z != null) bar(z)
+    bar(<!TYPE_MISMATCH!>z<!>)
+    bar(z!!)
+    if (z != null) bar(z<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/IfThenElseBothInvalid.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/IfThenElseBothInvalid.jet
new file mode 100644
index 00000000000..37f20e95089
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/IfThenElseBothInvalid.jet
@@ -0,0 +1,16 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    bar(<!TYPE_MISMATCH!>x<!>)
+    if (x != 2) {
+        if (x == null) return
+        2+<!SYNTAX!><!>
+    }
+    else {
+        if (x == null) return
+        2+<!SYNTAX!><!>
+    }
+    bar(x)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ObjectExpression.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ObjectExpression.jet
new file mode 100644
index 00000000000..74ed7fbbdc0
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ObjectExpression.jet
@@ -0,0 +1,10 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    val <!UNUSED_VARIABLE!>a<!> = object {
+        fun baz() = bar(if (x == null) 0 else x)
+        fun quux(): Int = if (x == null) <!TYPE_MISMATCH!>x<!> else x
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/QualifiedExpression.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/QualifiedExpression.jet
new file mode 100644
index 00000000000..94c36bb42c2
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/QualifiedExpression.jet
@@ -0,0 +1,13 @@
+fun baz(x: Int): Int = x + 1
+
+class A {
+    fun bar(x: Int) = baz(x)
+}
+
+fun foo() {
+    val x: Int? = null
+
+    A().bar(<!TYPE_MISMATCH!>x<!>)
+    if (x == null) return
+    A().bar(x)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Return.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Return.jet
new file mode 100644
index 00000000000..23f0379d1a7
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Return.jet
@@ -0,0 +1,12 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo(): Int {
+    val x: Int? = null
+
+    bar(<!TYPE_MISMATCH!>x<!>)
+    if (x != null) return x
+    if (x == null) return if (x != null) x else <!TYPE_MISMATCH!>x<!>
+    if (x == null) return x
+    if (x != null) return if (x == null) x else x
+    return x
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ThisSuper.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ThisSuper.jet
new file mode 100644
index 00000000000..c2b4ee9fdd2
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ThisSuper.jet
@@ -0,0 +1,21 @@
+open class Base {
+    fun bar(x: Int): Int = x + 1
+}
+
+class Derived : Base() {
+    fun baz(x: Int): Int = x + 1
+
+    fun foo() {
+        val x: Int? = null
+
+        super.bar(<!TYPE_MISMATCH!>x<!>)
+        this.baz(<!TYPE_MISMATCH!>x<!>)
+        if (x == null) return
+        super.bar(x)
+        this.baz(x)
+
+        val y: Int? = null
+        if (y != null) super.bar(this.baz(y))
+        else this.baz(super.bar(<!TYPE_MISMATCH!>y<!>))
+    }
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Throw.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Throw.jet
new file mode 100644
index 00000000000..e1e2ce8fd57
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Throw.jet
@@ -0,0 +1,10 @@
+fun bar(x: Int): RuntimeException = RuntimeException(x.toString())
+
+fun foo() {
+    val x: Int? = null
+
+    if (x == null || 1 < 2) throw bar(<!TYPE_MISMATCH!>x<!>)
+    if (x == null) return
+    throw bar(x)
+    throw <!UNREACHABLE_CODE!>bar(x)<!>
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/TryCatch.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/TryCatch.jet
new file mode 100644
index 00000000000..f3f8ce0347c
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/TryCatch.jet
@@ -0,0 +1,15 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+    
+    bar(<!TYPE_MISMATCH!>x<!>)
+    if (x == null) return
+    try {
+        bar(x)
+    }
+    catch (e: Exception) {
+        bar(x)
+    }
+    bar(x)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/UnaryExpression.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/UnaryExpression.jet
new file mode 100644
index 00000000000..8803f8d30bf
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/UnaryExpression.jet
@@ -0,0 +1,14 @@
+fun bar(x: Int): Int = x + 1
+fun baz(b: Boolean): Boolean = !b
+
+fun foo() {
+    val x: Int? = null
+
+    bar(<!UNSAFE_CALL!>-<!>x)
+    if (x != null) bar(-x)
+    bar(<!UNSAFE_CALL!>-<!>x)
+
+    val b: Boolean? = null
+    baz(<!UNSAFE_CALL!>!<!>b)
+    if (b != null) baz(!b)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/When.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/When.jet
new file mode 100644
index 00000000000..5582e7b2346
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/When.jet
@@ -0,0 +1,18 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    if (x != null) {
+        when (x) {
+            0 -> bar(x)
+            else -> {}
+        }
+    }
+
+    when (x) {
+        0 -> { if (x == null) return }
+        else -> { if (x == null) return }
+    }
+    bar(x)
+}
diff --git a/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/While.jet b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/While.jet
new file mode 100644
index 00000000000..8cf3c7b7df3
--- /dev/null
+++ b/compiler/testData/diagnostics/tests/dataFlowInfoTraversal/While.jet
@@ -0,0 +1,22 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+    while (x == null) {
+        bar(<!TYPE_MISMATCH!>x<!>)
+    }
+    bar(x)
+    
+    val y: Int? = null
+    while (y != null) {
+        bar(y)
+    }
+    bar(<!TYPE_MISMATCH!>y<!>)
+    
+    val z: Int? = null
+    while (z == null) {
+        bar(<!TYPE_MISMATCH!>z<!>)
+        break
+    }
+    bar(<!TYPE_MISMATCH!>z<!>)
+}